Urban Lake Management 797

Managing Lakes for

Pure Drinking Water

by Anne Kitchell

"Lakes are the reservoirs into which rivers

and other streams empty, and their waters are

not widely different from their sources of water

supply. They are the receptacles of all the waste

products of the inhabitants of the district; they

receive the contents of sewers, cess pools, and

privies; the offal of the distilleries, slaughterhouses and tanneries, and the refuse of factories."

Willis Tucker, 1885a

"In the United States, 30,000 people die

annually from typhoid fever. The mortality

from typhoid fever in many of the eastern cities

is proportional to the quantity of sewage which

enters the water supplies."

Floyd Davis, 1889

"In the absence of positive knowledge, we

had best err, if err we must, on the safe side, and

avoid the use of polluted waters."

Willis Tucker, 1885b

As these historical quotes remind us, public health

authorities have always had an acute interest in the

purity of their drinking water, an intuitive understanding of the watershed concept, and an aggressive pursuit

of ever-cleaner source waters. Over the past hundred

years, these trends have continued. If any threat to

source waters can be established, even imperfectly, and

a reasonable remedy to treat or eliminate the threat

found, it will usually be undertaken. Witness the progressive engineering “firsts” that have occurred in

water supply watersheds: storage reservoirs, filtration,

disinfection, wastewater treatment, watershed planning, land regulation, spill contingency plans, stormwater treatment practices and buffers, to name but a few.

Indeed, arguably the earliest known watershed ordinance was enacted in Chicago in 1833, when authorities declared it to be unlawful to throw or put into the

Chicago River... “any carcass of any dead animal or

animals, under a penalty of three dollars per offense”

(CBH, 1871).

The progressive adoption of these sanitary engineering strategies certainly ranks among the greatest

public health achievements of our era; outbreaks of

waterborne infectious diseases such as typhoid fever,

cholera, shigellosis and salmonellosis have virtually been

eliminated as a result. Still, the

quest to provide a pure supply of

drinking water never ceases, as

science continuously reveals

new risks to public health, such

as giardia, cryptosporidium, disinfection by-products, and a wide spectrum of pollutants and potential carcinogens.

In recent years, water supplies have gradually

recognized that improved water treatment, while necessary, is not sufficient by itself to protect public water

supplies. Watershed management is also needed to

protect source waters, particularly so for communities

growing outward into previously undeveloped water

supply watersheds.

This article reviews the current state of watershed practice in

reservoirs used for water supply. It

begins by reviewing some of the

unique concerns facing reservoir

managers in these watersheds, and

then reports on a detailed survey of

trends in watershed treatment practices used to protect more than 20

large water supply reservoirs in the

U.S. Finally, the article recommends ways in which

watershed practices could be improved to meet evertighter drinking water standards, and how recently

required source water assessment plans could be better

integrated into local watershed planning.

Impact of Watershed Development on Surface

Water Supplies

For much of this century, water supply reservoirs

were intentionally located in areas of little or no

watershed development. In the last three decades,

however, many communities have begun experiencing considerable growth pressures within the watersheds of their water supply reservoirs. Managers are

quickly realizing that they must clearly understand the

impact land development can have on the quality of

their source waters. This realization has been prompted

by increasingly tight drinking water standards under

the Safe Drinking Water Act (see Table 1 for a summary

Improved water treatment, while

necessary, is not sufficient by

itself to protect public water

supplies.
798 Urban Lake Management

of these new requirements), as well as by new research on

the impact of stormwater runoff on reservoir water quality. The following section reviews recent research on key

contaminants in reservoir watersheds.

Disinfection By-Products

Nearly all water supplies inject chlorine or bromine

to treated waters as an effective last line of defense

against pathogens. However, if the source water has high

concentrations of organic matter, the disinfection process can create a series of disinfection

by-products (or DBPs) under the right

conditions. These DBPs include up

to 30 different compounds such as

trihalomethanes (THMs), haloacetic

acids (HAAs) and chloroform, many

of which are suspected to adversely

affect human health.

Recent research has shown a

strong association between the consumption of treated water containing DBPs and the

occurrence of bladder cancer, and possibly rectal cancer.

By some estimates, as many as two to 17% of bladder

cancer cases in the U.S. and up to 14 to 16% of bladder

cancer cases in Canada could be attributed to the presence of DBPs in drinking water (King and Marret, 1996

and Wigle, 1998). While epidemiologists caution that

the research does not prove a causal relationship, the

strength of the relationship has prompted the EPA to

issue tougher rules on DBPs (US EPA, 1998).

DBPs present a severe challenge for reservoir managers, since they are formed at the end of the treatment

process, and few practical alternatives to disinfection

currently exist. The primary strategy for reducing DBPs

is precursor control, which in simple terms seeks to

reduce the amount of organic carbon in source waters

prior to treatment (particularly humic and fulvic acids,

NRC, 2000). In a practical sense, precursor control is

simply another name for watershed treatment to reduce

organic carbon and phosphorus loads to a reservoir.

Watershed development makes precursor control

very difficult for two reasons. First, stormwater runoff

from urban areas often dramatically increase phosphorus

loads delivered to a lake, and in turn, increase algal levels

(see Caraco and Brown, this issue). Decomposition of

algae in the reservoir can help drive up organic carbon

concentrations. Thus, the increased eutrophication that

often occurs in urban lakes creates an internal source of

organic carbon that make it difficult to control DBP

levels at the treatment plant. As a consequence, many

regulators are setting more stringent limits on the maximum amount of in-lake phosphorus or chlorophyll a

concentrations allowed with a water supply reservoir,

which often translates into limits on watershed phosphorus loadings. For example, some communities have

established in-lake chlorophyll limits ranging from

five to 15 ug/l and in-lake phosphorus concentrations

ranging from 0.01 to 0.05 mg/l. As Caraco (this issue)

observes, few urbanizing watersheds can meet such

limits given current watershed treatment technology.

The second reason why precursor control is difficult in urban watersheds is that stormwater runoff can

deliver significantly higher loads of both total and

soluble organic carbon, in comparison to other watershed land uses. Although not much data has been

historically collected on total organic carbon (TOC)

concentrations in urban stormwater runoff, the Center

recently derived a mean TOC concentration of 17 mg/

l (median 15.2, range: 5.3 to 41.3 mg/l) based on 19

urban catchments contained in a national STP monitoring database (Winer, 2000).

The primary source of TOC appears to be the

decomposition of leaf and other organic matter in

curbs, storm drains and streets, along with some

combustion by products. Data on dissolved organic

carbon (DOC), which is thought to be the main precursor for DBPs, are even more sparse in the stormwater

literature. A handful of studies suggest that DOC concentrations in the three to 7 mg/l range for untreated

stormwater runoff. Only three studies have monitored

DOC removal in stormwater ponds or wetlands, and

these suggest that they have little or no DOC removal

capability, and may actually increase DOC levels

(SWAMP, 2000). Meyer and Couch (2000) report that

annual DOC loads were higher in urban streams than in

forested or agricultural streams in the southeastern

Piedmont.

Turbidity

"It is believed that an excessive turbidity,

caused by sand or clay, is productive of intestinal difficulties, indigestion, dyspepsia and

diarrhea."

Davis, 1889

Turbidity has been used for more than a century as

a measure of water clarity and a standard for both the

purity of drinking water and the efficient operation of

filtration systems in drinking water treatment plants. In

addition, turbidity is also used as a surrogate measure

to predict pathogen removal. The EPA has recently

issued tighter standards on the permissible amount of

turbidity in drinking water, shifting from 1.0 to 0.3

NTUs (nephelometric turbidity units, see Table 1).

Watershed development greatly increases the turbidity to reservoirs in three distinct ways. First, turbidity increases as fine particles are washed off impervious

surfaces during storm events. The average turbidity of

DBPs present a severe

challenge for reservoir

managers, since they are

formed at the end of the

treatment process.
Urban Lake Management 799

Table 1. Condensed Summary of Recent Federal Drinking Water Regulations 

(NRC, 2000; US EPA, 2001a) 

Year Regulations Key Components 

1974 Safe Drinking Water Act 

(SDWA) 

• Contains provisions for assessing and preventing biological and 

chemical contamination of drinking water supplies 

• Targets specific contaminants in water supplies 

1986 SDWA Amendments • Regulates 83 specified contaminants 

• Sets goal of adding 25 new contaminants every three years 

Surface Water Treatment 

Rule (SWTR) 

• Requires filtration for all surface water systems unless it can be 

proven unnecessary 

• Outlines conditions for filtration avoidance based on source water 

quality, disinfection criteria and site-specific criteria 

• Improved treatment criteria for Giardia and viruses 

• Introduces metrics of log removal of microbes and CT (product of 

disinfectant concentration and contact time) as control parameter for 

disinfection 

1989 

Total Coliform Rule (TCR) 

• Criteria to prevent waterborne microbial diseases 

• Requires suppliers to test drinking water for harmful microorganisms 

• Set stringent limits on total coliform 

1991 Lead and Copper Rule 

(LCR) 

Requires increased evaluation of treatment processes used to control 

corrosion 

Information Collection Rule 

(ICR) 

 Mandates that suppliers collect water quality data to form a 

national database, particularly pathogens and DBPs 

1996 

SDWA Amendments 

Establishes Source Water Assessment Program (SWAP) to develop 

and implement a watershed approach to source water 

improvement/protection by delineating watersheds that supply drinking 

water and assessing their susceptibility to known contaminants 

Drinking Water 

Contaminant Candidate 

List (CCL) 

• List of 50 chemical and 10 microbiological (non-regulated) 

contaminants known/or anticipated to occur in drinking water 

• Prioritizes contaminants for future research, additional data needs, 

and as regulatory candidates 

Stage 1 

Disinfectants/Disinfectants 

By-Products Rule (D/DBP) 

• Updates MCLs for Total THMs; new MCLs for 5 HAAs, chlorite, and 

bromate and sets residual levels for chlorine compounds 

1998 • Sets levels for TOC as DBP precursor 

Interim Enhanced Surface 

Water Treatment Rule 

(IESWTR) 

• Requires tightening of turbidity requirements for filtered systems from 

0.5 NTU to 0.3 NTU 

• Final rule incorporates microbial benchmarking ; require systems to 

show that filtration and disinfection are reducing Cryptosporidium; 

requires unfiltered suppliers to amend watershed control programs to 

control for Cryptosporidium

Public Notification Rule 

Sets requirements for how and when public notification required; 

Notification required when water utility fails to meet drinking water 

standards, or is facing a public risk situation 2000 

Radionucleotides Final 

Rule 

• Sets MCL for uranium at 30ug/l 

• MGCL of 0 for all radionucleotides 

2001 Filter Backwash and 

Recycling Rule (FBRR) 

• Requires recycled filter backwash, sludge thickener supernatant, 

and liquids from dewatering process to be returned to 1st stage of 

direct filtration/treatment process 

• First attempt to govern backwash situation that may compromise 

microbial control 
800 Urban Lake Management

urban stormwater runoff typically ranges about 100 to

200 NTUs, according to the NURP study. The second

source of turbidity in urban watersheds comes from

sediments eroded from active construction sites. The

median turbidity in construction site runoff in Maryland

was reported to be about 450 NTUs (range: four to 8,200

NTUs). Even after effective erosion and sediment control

practices were applied to construction sites, median

turbidity still exceeded 200 NTUs (Schueler and Lugbill,

1990). The third source of turbidity in urban watersheds

is caused by stream channel erosion during large storm

events, with concentrations frequently ranging from 200 to 1,000

NTUs, depending on the intensity

of the storm event. While turbidity

levels in reservoirs often decline

due to dilution and settling, they

still represent a chronic problem

for drinking water treatment plant

operators.

Drinking water treatment plants can usually meet

the new turbidity standard even when their source waters

become highly turbid using a combination of coagulation, flocculation and filtration, but it is neither easy nor

inexpensive to do so. Plant operators must carefully

monitor the spikes or plumes of turbidity in the reservoir

after storms, and then administer the precise dose of

chemicals and filter run times to reduce them. As a result,

the cost of drinking water treatment increases, and the

reliability of treatment can decline within urban watersheds.

Loss of Reservoir Capacity

A more long term concern of watershed managers is

the gradual loss of reservoir capacity due to sedimentation. Urban land uses often produce higher sediment

loadings than other land uses, with the possible exception of agricultural row crops. How much reservoir capacity will be lost over time is usually a function of a

reservoir’s depth, and its drainage area to surface area

ratio (DA/SA). When a reservoir is relatively shallow, has

a DA/SA ratio of 50 or more and is highly urban, it is likely

that sedimentation could result in a significant loss of

capacity within a matter of several decades.

Pathogens

A pathogen is a microbe that is actually known to

cause disease under the right conditions. Examples of

bacterial pathogens frequently found in stormwater runoff include Shigella spp. (dysentery), Salmonella spp.

(gastrointestinal illness), and Pseudonomas auerognosa

(swimmer’s itch). Other species can cause cholera, typhoid fever and staph infections. The actual risk of

contracting a disease from a pathogen depends on a host

of factors such as the method of exposure or transmission,

pathogen concentration, incubation period and the

age and health status of the infected party.

Cryptosporidium and Giardia

In the last several decades, the two most common

waterborne diseases in the U.S. have been

cryptosporidium and giardia (NRC, 2000).

Cryptosporidium was the protozoan responsible for

the largest waterborne disease outbreak in the U.S.

(Fox and Lytle, 1996). To infect new hosts, these

protozoans create hard casings known as cysts (giardia) or oocysts (cryptosporidium) that are shed in

feces, and travel through surface waters in search of a

new host. The cysts or oocysts are very durable, and

can remain viable for many months.

Sand filtration at drinking water plants has not

been found to be fully effective in removing all cysts

and oocysts (LeChevallier et al., 1991, 1995), although it is not clear whether the cysts that pass

through sand filters remain viable. A series of studies

have found that back flushing of sand filters at drinking water treatment plants resuspend protozoa, and

can become a significant source of cysts/oocysts

(LeChevallier et al., 1995). Chemical disinfection can

inactivate cysts and oocysts, but typically requires

chemical pretreatment, higher doses, and longer contact times than when used to inactivate fecal coliforms.

Until recently, the major sources of protozoa in

surface waters were generally thought to be human

sewage, dairy runoff and wildlife. However, several

recent studies have detected high levels of both

cryptosporidium or giardia in stormwater runoff (Stern,

1996; Xiao et al., 2000, 2001). David Stern (1996)

monitored a series of agricultural and urban watersheds within the New York City water supply reservoir

system, and found urban subwatersheds had slightly

higher rates of giardia and cryptosporidium detection

than agricultural subwatersheds, and a higher rate of

confirmed viability. Graczyk and his colleagues (1998)

recently discovered that migratory Canadia geese

were a vector for both giardia and cryptosporidium in

the Mid-Atlantic region. It is intriguing to speculate

whether the large populations of resident geese found

in many urban ponds might be a source of

cryptosporidium transmission, and more research is

warranted.

Total and Fecal Coliforms

Public health authorities have traditionally used

total coliforms or fecal coliform bacteria as an indicator of potential microbial risk, and have set stringent

standards for both drinking water supplies and finished water (see Table 1). Watershed development

tends to greatly increase coliform levels in source

Several recent studies have

detected high levels of both

cryptosporidium or giardia in

stormwater runoff.
Urban Lake Management 801

waters. For example, the mean concentration of fecal

coliforms in urban stormwater runoff is nearly 15,000

counts per 100 ml (Schueler, 1999). The coliforms are

generated from a diverse set of sources in an urbanizing

watersheds, and may take many complex pathways to

reach a reservoir. For a complete discussion of urban

bacteria sources, the reader should consult Schueler

(1999).

Once coliforms reach a reservoir, they are subject

to die-off, and are further reduced by filtration and

disinfection at the drinking water treatment plant.

Nevertheless, the coliform loading in urban watersheds can make plant operations more expensive, and

can exacerbate the DBP problem if greater levels of

disinfection are needed to meet coliform standards.

Organic and Inorganic Chemicals

The U.S. EPA has established primary drinking

water standards for 69 different organic and inorganic

chemicals that are known or suspected to cause health

problems (US EPA, 2001a). Each of these chemicals has

a maximum contaminant level or MCL that must be

achieved in the finished water, and water utilities must

frequently monitor these levels.

Many of these organic and inorganic chemicals

have been detected in urban stormwater runoff or baseflow, but in most cases, they are present in concentrations

well below the MCL. Table 2 compares the median

pollutant concentrations in urban stormwater runoff

with the established MCL for finished drinking water.

With the exceptions of lead, turbidity and coliforms, the

median concentration of most pollutants found in urban

stormwater are about an order of magnitude lower than

the MCL. It is important to note that it is probable that

the maximum reported concentrations could equal or

exceed the MCL during some extreme runoff or snowmelt events.

The EPA has also identified several chemicals of

critical concern for which it is considering developing

MCLs as well. Several of these chemicals have been

detected in urban stormwater or streamflow, most notaTable 2. National Event Mean and Median Concentrations for Chemical 

Constituents of Stormwater and Maximum Contaminant Goals and Levels 

EMCs Constituent Units Source 

of Data Mean Median MCL1

Copper mg/l (1) 0.0133 0.0111 1.3 (a)

Lead mg/l (1) 0.0675 0.0507 0.015 (b) 

Cadmium mg/l (2) 0.0007 0.005

Chromium mg/l (3) 0.004 0.1 

Nitrate mg/l (1) 0.658 0.533 10 

Turbidity ntu (2) 50 1.0

Fecal Coliform col/100 

ml (5) 15,038 5% 

Atrazine mg/l (6) 0.000023 0.003 

Simazine mg/l (6) 0.000039 0.004 

Cryptosporidium cysts (7) 37.2 3.9 (c) 

Giardia cysts (7) 41.0 6.4 (c) 

(1) Smullen and Cave, 1998; (2) EPA, 1983; (3) Brush et al., 1995; (4) Barrett and Malina, 

1998; (5) Schueler,1999; (6) USGS, 1998 (baseflow); (7) Stern, 1996 

Shaded rows indicate contaminants found in significant concentrations in urban 

stormwater, which could potentially threaten maintenance of water quality standards. 

1 Maximum Contaminant Level (MCL) The highest level of a contaminant allowed in 

drinking water. MCLs are enforceable and are set as close to MCLGs as feasible using the 

best available treatment technology and taking cost into consideration. 

(a) Lead and copper are regulated by a Treatment Technique that requires systems to 

control the corrosiveness of their water. If more than 10% of tap water samples exceed the 

action level (1.3 mg/l for copper, and for 0.015 mg/l for lead), water systems must take 

additional treatment steps. 

EPA s surface water treatment rules require systems to meet the following criteria (as of 

January 1, 2002): 

(b) Turbidity: may never exceed 1 NTU and must not exceed 0.3 NTU in 95% of the daily 

samples in any month. 

(c) Cryptosporidium: 99% removal; Giardia lambia: 99.9% removal/inactivation 
802 Urban Lake Management

bly MBTE, diazinon, chloropyrifos and several other

pesticides (Table 3). The USGS (1999) detected one or

more pesticides in 99% of urban stream samples in a

recent national water quality assessment. They found

that insecticides and herbicides were detected more

often and at higher concentrations in urban streams than

any other watershed land use (including agriculture).

Taste and Odor

Various chemicals, organic carbon and algal growth

present in source waters can influence the taste and odor

of finished water, and consumers are often quick to

notice and complain about them. For this reason, the

EPA (2001b) has recently issued voluntary guidelines

about the taste, odor and appearance of drinking water.

Table 3 compares the typical concentrations for some of

these pollutants found in urban stormwater runoff against

these recommended limits. With the possible exception

of chloride levels in snowmelt runoff, most urban pollutants remain below the established limits. It is important

to note that the greater algal growth, turbidity, and

organic carbon found in urban source waters can impart

disagreeable tastes and odors to finished water, often as

a result of the greater treatment required at the plant.

Spills, Leaks and Accidents

Urban development can increase the risk of spills,

leaks and accidents in a reservoir watershed, whether it

be a tanker accident discharging into a highway storm

drain, the derailment of a train carrying hazardous wastes,

a fire at an industrial site, a shutoff valve breaking on a

pipeline or storage tank, a slowly leaking landfill, pesticides dumped in a storm drain or any number of other

nightmare scenarios. In a larger urban watershed, it is

usually not a matter of whether one of these scenarios

will happen, but when, and how quickly the utility can

react to it. It is for this reason that nearly every utility

has developed contingency plans for spill response,

and often seeks to restrict or exclude as many of these

risks as possible within a watershed.

Watershed Management for Water Supply

Reservoirs

Given the potential impact of watershed development on the quality of water supply reservoirs, it is not

surprising that most communities have sought to strictly

regulate how and where new development occurs in

water supply watersheds. Under the Safe Drinking

Water Act, communities must perform a Source Water

Assessment for surface and subsurface water supplies

to identify potential sources of contamination for

water supplies. It is interesting to note that of the 33

sources of potential water contamination that the EPA

has recommended for investigation as part of this

assessment, 55% are directly or indirectly associated

with urban development in a watershed (see Box 1).

Clearly, communities will need to greatly improve the

effectiveness of watershed practices in reservoir watersheds where growth and development are anticipated.

The following section analyzes some of the key trends

in managing reservoirs watersheds across the country.

Survey of Watershed Practices in Water Supply

Reservoirs

The Center intensively surveyed 22 surface water

supply reservoirs, out of a total of 900 surface water

supplies of similar size in the country (van der Leeden

et al., 1990). The purpose of the survey was to examine

Table 3. Potential Pollutants of Concern Based on Concentration and 

Detection in Urban Stormwater 

Constituent Units Source 

of Data 

Median 

EMCs 

Concentrations of 

Concern

Total Dissolved 

Solids mg/l various 150 500 a

Zinc mg/l (1) 0.129 5 a

Chloride (snowmelt) mg/l (2) 116 250a

Organic Carbon mg/l (3) 11.9 4 b

MTBE ug/l (4) 1.6 20 to 40 c

Diazinon mg/l (5) 

(6) 

0.00025 

0.0055 0.0006 c

Prometon mg/l (5) 0.00031 0.001 c 

(1) Smullen and Cave, 1998; (2) Oberts, 1994; (3) CWP Database, unpubl.; (4) Delzer, 1996; (5) 

USGS, 1998 (baseflow); (6) Brush et al., 1995 a

 Secondary Maximum Contaminant Level (SMCL) Aesthetic guidelines to assist public water 

systems in managing their drinking water. 

b

 EPA Disinfection By-Products Rule -- <2mg/l TOC for treated water and <4mg/l in source water 

 c Contaminant Candidate List (CCL) EPA list of contaminants known or anticipated to occur in 

public water systems, and may require future regulations under the Safe Drinking Water Act 
Urban Lake Management 803

trends in watershed management for surface water

supplies across the country, and to identify innovative

practices to protect drinking water supplies from

watershed development. While our survey sample encompassed less than 3% of surface water supplies of

similar size nationally, it still represents the most

widespread survey of watershed practices for surface

water supplies since Robbins et al. (1991). We used the

following criteria to select our sample of reservoir

watersheds:

1. The reservoir must be used primarily as a source

of drinking water

2. The reservoir must serve a population greater

than 50,000

3. The contributing watershed must currently be

experiencing land development

4. Respondents in the watershed must be willing to

supply detailed information and review our case

studies for accuracy

It should be noted that over 10,000 smaller surface

water supplies exist in the U.S., and that these survey

results may not be transferable to these smaller reservoirs. The basic profile of our reservoir sample is

provided in Table 4, and its geographical representation is provided in Figure 1. More details on the survey

results and individual case studies can be found in

Table 5 and in Kitchell (2001).

The service population of the reservoir watersheds

ranged from 60,000 to seven million (median: 450,000).

Most of the reservoir watersheds had experienced

relatively modest development, with a mean of 8.5%

impervious cover (range two to 21%). The actual

amount of watershed development is probably somewhat higher, given that only half of the reservoirs

surveyed had recent land cover data for their contributing watersheds, and very few explicitly tracked impervious cover over time as an index of watershed

development.

Less than 20% of the reservoir watersheds were

completely contained within a single local political

jurisdiction; the mean number of local jurisdictions

was 4.8. About a third of the reservoir watersheds had

adopted some form of intergovernmental agreement or

legislation that formally established how the local

jurisdictions would cooperate together to protect the

water supply. The majority of reservoirs utilized filtration, although three unfiltered water supplies were also

analyzed.

Watershed Planning and Management

Surprisingly, only 10% of the reservoir watersheds were covered by a comprehensive watershed

management plan. Instead, most localities relied on a

progressively stringent series of ordinances, regulations

and zoning actions adopted over several decades. A

major reason for the lack of comprehensive watershed

planning was the need to coordinate among a large

number of political jurisdictions and the traditional

disconnect between the water utilities who are responsible for meeting drinking water standards and local

government(s) who are responsible for regulating land

use change in the watershed. On the positive side, water

utilities exercised some form of local development review authority in about a third of the surveyed watersheds.

Watershed Zoning

Zoning was the primary planning tool to protect the

water supply, and this tool was utilized in more than 90%

of the reservoir watersheds surveyed. Large lot residential zoning was the primary planning tool relied on to

reduce the overall density in the watershed. For example,

68% of the reservoir watersheds restricted development

to lots of one acre or more in size. In addition, 48% of

reservoir watersheds directly or indirectly excluded

commercial or industrial development through their

current zoning. Even where these uses were allowed,

they were a minor component of the watershed land use

distribution.

Box 1. Partial List of Potential Sources of Contamination 

Found in Wellhead Protection Areas and in Watersheds 

Related to Watershed 

Development: 

Atmospheric deposition 

Collection system failure 

Combined sewer overflow 

Construction 

Erosion from derelict land 

Habitat modification 

Highway maintenance and runoff 

Industrial point sources 

Land disposal 

Leaking underground storage 

 tanks 

Marinas and recreational boating 

Municipal point sources 

Salt storage sites 

Sewer line (leaking) 

Spills (accidental) 

Urban runoff/storm sewers 

Waste storage/storage tank leaks 

 (above ground) 

Not Development Related: 

Agriculture 

Contaminated sediment 

Debris and bottom deposits 

Domestic water lagoon 

Groundwater loadings 

Groundwater withdrawal 

Internal nutrient cycling 

Natural sources 

Recreation and tourism 

 activities 

 (other than boating) 

Resource extraction 

Sediment resupsension 

Silviculture 

Sources outside state 

 Jurisdiction or borders 

Unknown source 

Source: US EPA, 1998 
804 Urban Lake Management

Overlay districts were the preferred mechanism to

guide and regulate land use in the reservoir watersheds

(60%), whereas regular zoning was used in the remaining

watersheds. Overall, nearly 40% of

all reservoir watersheds had downzoned portions of the watershed to

reduce the overall intensity of development. No reservoir watershed reported that they had established a

watershed-wide impervious cover

limit, although about 38% had imposed stringent impervious cover

limits for individual lots.

A unique element of water supply watersheds is that

they often exclude or restrict certain land uses or activities that pose a potential water pollution risk or hazard.

Eighty percent of surveyed watersheds excluded one or

more land uses or activities, including the following:

Frequently Excluded

• New point source discharges

• Commercial or industrial land uses that generate, store

or dispose of hazardous wastes

• Any commercial or industrial development

• Above or below ground petroleum storage tanks

• Land application of sewage sludge

• New landfills or solid waste disposal facilities

• Confined animal feeding operations

Less Frequently Excluded

• Gas stations, service stations, junkyards

• Dry-cleaning establishments

• Golf courses

• Use of reclaimed waters

• Cemeteries

• Asphalt and concrete plants

• Combined sewers

• Sewer extensions

• Septic systems

• Sale of detergents that contain phosphorus

 About a third of the sampled watersheds emphasized stormwater runoff treatment over land use control

as the major thrust of their watershed protection strategy.

These communities tended to allow more development

in the watershed in exchange for more stringent phosphorus limits for runoff from individual sites.

Land Conservation

Land conservation was a major watershed protection strategy for all of the reservoir watersheds. This is

reflected by the fact that forest cover was the dominant

watershed land use in nearly all of the reservoir watersheds (Mean 50%: range five to 95%). In general, a

large fraction of forest or open space had been acquired

over time by the water utility or municipality, although

there was a great deal of variability in how much land

was retained in public ownership, as shown here:

• 48% owned less than 10% of watershed land

• 19% owned from 10 to 25% of watershed land

• 33% owned more than 25% of watershed land

Shoreline buffers were the key priority for land

acquisition in the reservoir watersheds, as 90% of the

reservoir watersheds reported that they owned and

managed extensive areas of shoreline buffer. These

publicly owned buffers ranged in distance from 150 to

2000 feet from the reservoir shoreline.

It is also interesting to note that 72% of reservoir

watersheds were still actively acquiring land or obtaining conservation easements. In many cases, the continued land acquisition was being used as a defensive

strategy to counter rapid watershed development.

Shoreline and Stream Buffers

Every reservoir in the survey either owned the

shoreline buffer or required extensive shoreline buffers

for new development. In addition, 90% of the watersheds also required buffers on tributary streams to the

reservoirs. The median width of shoreline buffer was

150 feet, but the range was very wide: from 25 to 2,000

feet. In general, the widest shoreline buffers were owned

by a municipality or utility. The median buffer for

tributary streams was 100 feet (range: 25 to 500 feet).

The shoreline buffers often had specific vegetative

targets (70%), and a wide range of prohibited or restricted uses within the shoreline buffer (80%). A list of

the more common uses excluded from shoreline buffers

includes the following:

• Impervious cover

• Septic tanks or drain fields

• Clear cutting

• Structures

• Commercial or industrial parking lots

• Grazing or livestock

• Land disturbance

• Pesticide application

• Generation, storage or disposal of hazardous

 materials

In many cases, continued

land acquisition was being

used as a defensive strategy

to counter rapid watershed

development.
Urban Lake Management 805

Table 4: General Characteristics of Drinking Water Watersheds Surveyed 

Watershed 

Reservoir Name Area 

(mi2

)

(%) 

Impervious 

Political 

Entities 

Drainage/

Reservoir 

Surface 

Area Ratio 

 Unfiltered Supply 

Wachusett, MA 111 1.6 1 9 17.9 

Croton Reservoirs, NY 374 -- 21 7.7 

Kensico, NY 13.2 19 5 4.0 

 Filtered Supply 

Dog River, GA 78 5.0 4 221.9 

Heads Creek, GA 27 11 2 38.4 

University Lake, NC 30 4.5 3 90.1 

Swift Creek (Lake Benson), NC 66 9 5 93.9 

Lee Hall, VA 14.2 6.5 2 18.4 

Occoquan, VA 592 12.01 6 210.5 

South Fork Rivanna , VA 258 5.7 1 1 423.4 

Swift Creek, VA 65 5-10 2 24.5 

Loch Raven, Pretty Boy, & Liberty, MD 466 -- 6 42.6 

Patuxent Reservoirs, MD 132 4 1 4 52.8 

Hoopes, DE 1.9 6.0 1 1 6.4 

Hemlocks, Easton, &Trap Falls, CT 91 -- 12 -- 

Lake Vadnais, MN 23 17.0 8 9.1 

Lake Whatcom, WA 57 <5 2 7.3 

Nicasio, CA 36 < 5 1 26.5 

Sweetwater, CA 184 21 1 -- 

Lake Dillon, CO 329 << 5 4 65.6 

Lake Austin,TX 41 10 1 4 16.4 

Town Lake, TX 158 13 1 5 224.2 

Notes: 

1 Actual impervious values; remaining values were estimated by survey respondent or the Center

Figure 1. Reservoir Locations
806 Urban Lake Management

It should be noted that septic systems were often

required to be located well outside of the designated

shoreline buffer zone in many reservoirs. In general,

shoreline and stream buffers used to protect water supplies were consistently more stringent than buffer requirements used to protect other water resources, as

reported in a national survey of stream buffers (Heraty,

1992).

Better Site Design

Better site design refers to a series of design techniques that reduce the impervious cover and increase the

natural cover associated with individual development

sites. Nearly 70% of the reservoirs

surveyed reported that they encouraged better site design in their watersheds, although the same proportion

indicated that they could do much

more in this respect. The two most

common better site design techniques

applied in reservoir watersheds were

open space or cluster subdivisions

(48%) and capping impervious cover for residential lots

(38%). Many of the residential impervious cover limits

were quite low (median: 12%; range: six to 30%).

It is interesting to note that these two better site

design techniques can work against each other. In practice, however, many reservoir watersheds exempted cluster subdivisions from impervious cover limits if it could

be demonstrated that the total impervious cover for a

subdivision would be lower with clustering than without

it. What is more important, many localities were willing

to extend sewers or allow shared septic systems in order

to make cluster development feasible.

Erosion and Sediment Control

Erosion and sediment control (ESC) practices during new construction were required in every reservoir

watershed in our survey. However, ESC performance

requirements were no more stringent in a reservoir watershed than in the surrounding locality 75% of the time.

Slightly more than a third of localities (36%) did report

more stringent requirements in regard to ESC plan review or inspections. Many of these localities shared

development review and inspection authority with the

water utility.

Stormwater Treatment Practices

Treatment of stormwater runoff quality was required

in all but one of the reservoir watersheds surveyed. It was

also noteworthy that 64% had more stringent stormwater

requirements within the reservoir watershed than in the

surrounding locality. In addition, 71% of the reservoir

watersheds indicated that they had started or were planning to start a stormwater retrofit program to treat runoff

from existing development.

Requirements for New Development

In general, reservoir watersheds require designers

to treat a greater volume of stormwater runoff than nonreservoir watersheds. Sizing requirements ranged from

one to two watershed inches of treatment, which is

about twice the typical treatment volume used elsewhere. Wet ponds were the most frequently used type

of stormwater treatment practice in reservoir watersheds. About 25% of the reservoir watersheds required

designers to meet a specific phosphorus removal target. Examples of these targets include the following:

• 0.22 lbs/ac/yr

• 50 to 65% phosphorus removal

• Maintenance of predevelopment phosphorus

 loading

Only a handful of reservoir managers reported that

they inspected stormwater treatment practices more

frequently within a reservoir watershed.

Treating Existing Development

Stormwater retrofitting is becoming an increasingly common practice to treat existing developed

areas within reservoir watersheds. For example, 38% of

the reservoir watersheds had actually installed stormwater retrofits to improve the quality of runoff from

existing development, and another 33% were considering pursuing a stormwater retrofit strategy. However,

with the notable exception of the Kensico Reservoir,

most watersheds had retrofitted only a small fraction of

existing developed areas to date.

Wastewater Management

Surface Wastewater Discharges

New wastewater discharges were explicitly prohibited in 85% of reservoir watersheds. Three watersheds did have major wastewater discharges to the

reservoir, but each relied on advanced tertiary treatment. Nearly all of the reservoirs used sewers to collect

wastewater from at least a portion of their watersheds,

but 85% pumped the sewage out of the watershed.

Further, a third of the reservoir watersheds reported that

they had extended sewers to relieve areas prone to

failing septic systems.

Septic Systems

Septic systems were extensively utilized in about

67% of the surveyed watersheds. They were discouraged or prohibited in 14% of our sample. Many responTreatment of stormwater runoff

quality was required in all but

one of the reservoir watersheds

surveyed.
Urban Lake Management 807

Table 5. Survey Results (n =17-22)

Watershed Protection Measure %yes Watershed Protection Measure %yes 

Watershed Planning Erosion and Sediment Control 

Have comprehensive watershed plan 10% Require ESC during construction 100% 

Utilize zoning as primary land use tool 90% Have more stringent ESC criteria for 

reservoir protection 26% 

Have protection overlay district 60% Report more intensive review or inspection 

inside watershed 36% 

Use large lot zoning (1 acre or more) 68% 

Rely primarily on stormwater treatment practices 32% Stormwater Treatment 

Exclude specific uses/activities from watershed 80% Require stormwater treatment 95% 

Exclude new commercial or industrial uses 

(directly or by zoning) 48% Have more stringent criteria for water 

supply watershed 64% 

Have down zoned portions of watershed 37% Require designer to meet specific 

phosphorus removal target 25% 

Requirements take distance to intake into 

account 42% Require specific practices or larger 

treatment volumes 67% 

Dominant land use is forested/open space 59% Have installed retrofits for existing 

development 38% 

Dominant land use is commercial/industrial 5% Are considering pursuing a retrofit strategy 33% 

Have recent land use data (since 1996) 55% 

Track impervious cover 37% Non-Stormwater Discharges 

Have septics in watershed 100% Land Conservation 

 Have sewers in watershed 95% 

> 10% of watershed owned by utility/public 48% Have reservoir specific criteria for septics 76% 

10-25% of watershed owned by utility/public 18% Require minimum septic setbacks at least 

100ft 89% 

>25% of watershed owned by utility/public 33% Mandate inspections/cleanout 46% 

Have a land acquisition/conservation easement 

program 

72% Exclude wastewater discharges from 

watershed 86% 

Regulate hazardous material 

storage/disposal/generation in watershed 73% Shoreline and Tributary Buffers 

 Report having a spill contingency plan 95% 

Require or own shoreline buffer 100% 

Require tributary buffers 90% Stewardship 

Minimum shoreline buffer is greater than 100ft 80% Monitor tributary and watershed lands 90% 

Minimum tributary buffer is greater than 100ft 50% Some form of education and outreach for 

watershed stewardship 86% 

Specify vegetative targets for buffer area 70% Prohibit swimming in reservoir 90% 

Specify allowable or prohibited uses 85% Prohibit gasoline engines in reservoir 90% 

 Restrict public access to reservoir 27% Better Site Design 

Mandate impervious cover at the site 38% 

Mandate BSD in watershed 4% 

Have active clustering/open space development 48% 

Encourage BSD 68% 

Admit that they could do more 65% 

 
808 Urban Lake Management

dents indicated concerns about septic systems as a possible pollutant source, and nearly all had developed

reservoir-specific regulations for them. The most frequent regulations included larger setbacks, that ranged

from 50 to 600 feet in distance. Just less than half of the

reservoir watersheds required mandatory inspection and

pumpouts. In addition, many of the reservoirs recently

adopted innovative programs to improve the performance of septic systems in their watersheds, including

the following:

• Free inspections

• Requirements for non-discharge units

• Reservoir setbacks of up to 600 feet

• Requirements that innovative septic systems be used

with higher nitrogen removal capability

• Proof of pumpout required to maintain public water

service

• Utility monitoring to detect failing systems

• Sewering of failed septic systems

• Drain field rotation

Watershed Stewardship

Watershed Education

While 86% of the surveyed reservoirs reported that

they had some kind of watershed education program,

most were relatively modest in scope.

For example, less than half of the

outreach programs devoted full-time

staff to watershed education. Even

fewer had developed an overall strategy to guide their watershed outreach efforts (e.g., targeting specific

watershed behaviors or conducting

pollution prevention training).

Spill Response

The potential risk of spills or leaks of hazardous

material in the watershed has always been a concern for

reservoir managers. More than 90% of the surveyed

watersheds reported that they had developed and tested

a spill contingency plan. In most cases, these plans

focused on potential spills from transportation corridors,

such as highways or railroads. Most reservoir watersheds

(76%) regulated the generation, storage and disposal of

hazardous wastes within their watershed, usually by

excluding these types of industrial uses, or requiring

setbacks from the shoreline. However, few reservoirs had

any kind of reporting program to track existing sources

of hazardous materials in the watershed.

Monitoring

Robbins et al. (1991) noted that few reservoir

watersheds were monitoring their watersheds and tributary streams, but this has changed greatly in the last

decade. According to our survey, 90% of the reservoir

watersheds indicated that they were monitoring within

their watersheds and tributary streams. Only a handful,

however, reported that they were monitoring the effectiveness of treatment practices, such as stormwater

ponds.

Reservoir Restrictions

Reservoir managers often restrict public access to

the reservoir itself. While only 27% of survey respondents indicated that they completely prohibited public access to the reservoir, nearly all of the reservoirs

restricted access or use in some manner. The most

common restrictions were to prohibit swimming (90%)

and the use of gasoline engines within the reservoir

(90%).

Overall Findings

Based on our survey, it is evident that nearly all

reservoirs apply the eight watershed protection tools

described above, at least in some form (Figure 2). Water

supplies have traditionally been heavily regulated,

given the paramount public health concern and increasingly stringent drinking water standards. It is fair

to say that no other kind of watershed has regulated

development to the extent seen in water supply watersheds.

Given this, it is surprising that only 10% of the

reservoir watersheds had developed a comprehensive

watershed plan. And despite the fact that development

was expected to continue in nearly all of the watersheds, none had established a maximum upper limit on

the total amount of watershed development that could

occur in the future. This shortcoming reflects the disparity between water utilities who want clean source

water and local government(s) who want growth, and

are responsible for regulating land use in the watershed. Still, the lack of watershed land use planning is

disturbing, given that watershed development is at the

root of most potential sources of drinking water contamination.

And indeed, many reservoir managers acknowledged shortcomings in their watershed management

programs. Most notable were consistent concerns about

the long term maintenance of stormwater practices,

septic systems, and buffers. Others reported chronic

problems with the actual implementation of watershed

practices in the field. The cumulative impact of inadequate staffing, waivers, infrequent inspections, poor

We recommend that every

source water assessment

measure the amount of current

watershed impervious cover.
Urban Lake Management 809

90%

72%

90%

68%

100%

95%

86%

73%

90%

86%

0% 20% 40% 60% 80% 100%

Water Supply Watershed Protection Tool

Percentage of Survey Respondents

Utilize zoning as primary tool for protecting water supply 

Have a land acquisition/conservation easement program 

Require both shoreline and tributary buffers 

Encourage better site design techniques 

Require erosion and sediment control during construction 

Exclude wastewater discharges from watersheds 

Regulate hazardous mat. storage/generation/disposal 

Monitor tributaries and watershed lands 

Provide some form of public education 

Require treatment of stormwater runoff 

design standards and limited enforcement was believed by many to compromise the overall effectiveness of watershed protection programs. Some managers also lamented the lack of actual performance data

for watershed treatment practices, at both the site and

watershed level.

Integrating Watershed Planning Into Source

Water Protection

One of the key requirements of the 1996 Safe

Drinking Water Act Amendments is for water providers

to conduct a source water assessment plan (SWAP) to

identify potential contaminants, and then develop a

source water protection plan (SWPP) to minimize

these risks. Most states have just developed guidance

on the minimum elements that water providers need to

incorporate into these plans (see also a national manual

developed by NEIWPPC, 2000). The major components of a SWPP are public involvement, use of regulatory and non-regulatory practices to manage drinking water contaminants and adoption of spill response

contingency plans.

While state and federal water regulators clearly

endorse a watershed approach for developing SWPPs,

and, in particular, promote stakeholder involvement

and intergovernmental partnerships (US EPA, 1999),

they do not mandate that the cumulative impact of

current or future watershed development be explicitly

considered in the planning process. As a consequence,

it is not likely that many water providers will be able to

develop effective watershed land use plans. To some

extent, this reflects the fact that not all reservoir watersheds are experiencing development, and both water

regulators and water providers are reluctant to interfere

with the land use prerogatives of local governments.

We recommend that every source water assessment

measure the amount of current watershed impervious

cover, and forecast the amount of new impervious cover

to be created over the next 20 or 30 years. If current or

future impervious cover is expected to exceed 10% in the

watershed, we strongly recommend that communities

adopt more stringent treatment practices for new development. Table 6 summarizes the critical elements of a

source water protection plan we recommend for water

supply watersheds expected to exceed 10% impervious

cover. These recommendations are based on results from

the watershed population we surveyed; smaller systems

may want to take a simpler approach. These recommendations are a general framework to integrate watershed

management into source water protection plans, and

should be modified for unique watershed conditions

such as unfiltered supplies, lake geometry, and amount

of impervious cover.

Figure 2. Percentage of Survey Respondents Utilizing Watershed Protection Tools
810 Urban Lake Management

Table 6. Elements of a Source Water Protection Plan for Urban Surface Water Supplies

Watershed Protection

Tool More Than 10% Watershed Imperviousness

Watershed Planning,

Management and

Zoning

Adopt a comprehensive watershed plan that can provide consistent

implementation across all jurisdictions

Establish an ongoing watershed management structure

Update land use and development trend analysis track land use and

impervious cover every four years.

Designate a watershed manager for the reservoir

Create a reservoir protection overlay district and/or ordinance (see

Cappiella and Schueler, this issue)

Exclude or restrict pollutant hotspots (i.e industry, WWTP, and land fills)

Establish maximum level of watershed development/impervious cover

Land Conservation

Prioritize land acquisition to critical water supply protection areas (i.e.

corridors, streams, and intakes)

Maintain rural land through conservation easements

Shoreline and Tributary 

Buffers

Require, or acquire, wide shoreline (minimum 300 ft) and tributary

(minimum 125 ft.) buffers

Maintain natural shoreline vegetation and establish allowable uses

Better Site Design Set impervious cover caps for individual zoning categories

Allow cluster design for residential subdivisions to conserve open space

Erosion and Sediment

Control

Make inspection and enforcement efforts more stringent for construction

sites 

Stormwater Treatment

Practices

Size and design stormwater treatment practices for maximum

phosphorous removal

Use environmentally-sensitive design on lake-front properties to

minimize creation and concentration of stormwater runoff (see Cappiella

and Schueler, this issue)

Consider retrofitting existing development where necessary

Wastewater

Management

Prohibit new WWTP discharges in watershed; require advanced tertiary

treatment of existing discharges or pump out of watershed

Enforce tighter regulations for septic system design, siting, and

maintenance if non-sewered development allowed

Perform regular surveys to identify failing septic systems

Establish minimum 150 ft setbacks from tributaries 

Mandate regular clean out and inspection of septic systems

Watershed Stewardship

Expand monitoring efforts to include tributary monitoring and watershed

land assessments

Target education efforts towards relevant pollution prevention activities

such as lawn care and contractor education for proper fertilizer and

pesticide usage

Establish a spill response contingency plan and tracking system for

existing sources

Restrict recreational activities and gas motorboats
Urban Lake Management 811

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