U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2008–3033

May 2008

In cooperation with the City of Houston

Watershed Influences and In-Lake Processes—A Regional-Scale Approach to 

Monitoring a Water-Supply Reservoir, Lake Houston near Houston, Texas 

Created in 1954 by an impoundment on the San Jacinto 

River, Lake Houston currently (2008) supplies about 20 percent 

of the total source water for the city of Houston. Houston 

historically has relied on ground water as the major source 

of supply. As a result of regulations to limit ground-water 

withdrawals because of associated land subsidence (effective in 

2010), the lake will become the primary source of water supply 

for the city in the future (Harris-Galveston Coastal Subsidence 

District, 1999). 

Since 1983 the U.S. Geological Survey (USGS), in cooperation with the City of Houston, has collected water-quality 

and lake-level data at Lake Houston, as well as discharge and 

intermittent water-quality data at its major inflowing tributaries. 

Previous studies indicate that Lake Houston is shallow, eutrophic, light limited and has a variable hydrologic regime with 

water residence times ranging from 12 hours to 400 days (Lee 

and Rast, 1997; Liscum and East, 2000). Spring Creek, a tributary that drains the western, more urban, part of the Lake Houston watershed, contributes more sediment and nutrients than 

East Fork San Jacinto River, a tributary that drains the more 

rural, eastern part of the watershed (Sneck-Fahrer and others, 

2005). This fact sheet explains the importance of monitoring for 

management of the resource and describes ongoing research in 

the Lake Houston watershed by the USGS and the City.

The Importance of Monitoring for Source-Water 

Protection and Water-Supply Operations

With increased demand for Lake Houston water, a comprehensive understanding of the factors that affect water quality 

in the lake is needed. Because of the proximity of the lake to 

Houston, the effects of urbanization on the water quality of the 

lake and its tributaries are of particular concern. Urbanization 

might cause changes in stream hydrology that decrease water 

residence times in the lake and increase sediment and nutrient 

loads to the lake. Increased nutrient loads to Lake Houston can 

cause an increase in plant growth and decay (eutrophication), 

which decreases dissolved oxygen concentrations and thereby 

degrades water quality and biological communities. 

Real-time water-quality monitoring of the tributaries 

and the lake allow observation of the timing of large inflows 

and resulting effects on in-lake processes that might affect 

source-water quality. Tracking inflows through the lake can 

give water-treatment facility operators time to respond to 

changes in source-water quality. Of particular concern in Lake 

Houston are inflows that might adversely affect taste and odor 

of the water.

Ongoing Research in the Lake Houston 

Watershed

Because of the need for a scientifically based source-water 

protection plan for Lake Houston, the USGS, in cooperation 

with the City of Houston, has established monitoring stations in 

the Lake Houston watershed to evaluate the effects of watershed 

influences and in-lake processes on Lake Houston water quality. 

The watershed has been monitored since 2005 using two continuous water-quality monitoring stations, one in the more rural 

eastern part of the watershed and the other in the more urban 

western part. Since 2006, Lake Houston has been monitored at 

three sites (for example, fig. 1) in the southern part of the lake.

Monitoring the Contributing Watershed

Real-time continuous monitoring of the watershed (fig. 2) 

provides hourly data on physical water-quality properties 

such as dissolved oxygen, pH, and temperature. The real-time 

water-quality monitors on the tributaries give an early warning of water-quality changes that might be about to occur in 

the lake. For example, during an October 2006 inflow, elevated 

turbidity in the tributaries was observed about 24 hours before 

turbidity increased at a site in the lake (fig. 3). During periods 

of increased flow into Lake Houston, actinomycetes bacteria in 

storm runoff might cause taste-and-odor problems. The realtime tributary data inform water treatment facility operators of 

impending changes in water quality of the lake and give them 

lead time to adjust water treatment accordingly.

Figure 1. USGS lake water-quality monitoring station 

295554095093401, Lake Houston near Mouth of Jack’s Ditch.
Monitoring Lake Houston

Three real-time water-quality monitoring stations (fig. 2) 

with vertical profiling capabilities were installed at three 

sites in the lake in 2006. These stations provide continuous 

water-quality data from multiple depths in the lake as well as 

atmospheric data. Each station consists of a multiparameter 

instrument that measures temperature, specific conductance, 

pH, dissolved oxygen, turbidity, chlorophyll, and light. The 

real-time data collected on the lake provide information that can 

enhance understanding of the in-lake chemical and biological 

processes that affect Lake Houston water quality. For example, 

the data can indicate periods of low dissolved oxygen concentration (fig. 4), which facilitate the release of manganese and 

nutrients from lake-bottom sediment. High concentrations of 

manganese might cause taste-and-odor problems (Rasmussen 

and McAllister, 2005), and the release of nutrients, particularly 

phosphorous, might stimulate the growth of algae that produce 

compounds that cause undesirable taste and odor (Wetzel, 

2001). Discrete, multidepth, water-quality samples also are 

being collected and analyzed on a biweekly-to-monthly basis to 

complement and verify the real-time data.

A comprehensive understanding of the processes affecting 

water quality is required to develop effective best-management 

practices and source-water protection plans. Combined, the 

watershed and lake monitoring will increase the understanding of the effects of inflows, nutrient and sediment loads, and 

water-column structure on the chemistry and biology of Lake 

Houston. Knowledge gained from these studies will help ensure 

that Lake Houston remains a sustainable source of water supply 

for Houston.

All continuous real-time data collected as a part of this 

program are available through the USGS National Water 

Information System Web Interface (NWISWeb) for Texas at 

http://waterdata.usgs.gov/tx/nwis/rt/. 

References

Harris-Galveston Coastal Subsidence District, 1999 [amended 2001], 

District regulatory plan: accessed January 8, 2008, at http://www.

hgsubsidence.org/Assets/PDFDocuments/HGRegPlan.pdf

Lee, R.W., and Rast, Walter, 1997, Light attenuation in a shallow, turbid reservoir, Lake Houston, Texas: U.S. Geological Survey Water 

Resources Investigations Report 97–4064, 33 p.

Liscum, Fred, and East, J.W., 2000, Estimated effects on water quality 

of Lake Houston from interbasin transfer of water from the Trinity 

River, Texas: U.S. Geological Survey Water Resources Investigations Report 00–4082, 50 p.

Rasmussen, P.P., and McAllister, D.H., 2005, Monitoring the water 

quality of Lake Olathe, Johnson County, Kansas: U.S. Geological 

Survey Fact Sheet 2005–3093, 2 p.

Sneck-Fahrer, D.A., Milburn, M.S., East, J.W., and Oden, J.H. 2005, 

Water-quality assessment of Lake Houston near Houston, Texas, 

2000–2004: U.S. Geological Survey Scientific Investigations Report 

2005–5241, 55 p.

Wetzel, R.G., 2001, Limnology (3d ed.): San Diego, Academic Press, 

1,006 p.

—Timothy D. Oden and Jennifer L. Graham 

For additional information, contact 

Director

USGS Texas Water Science Center

World Wide Web: http://tx.usgs.gov/ 

E-mail: gs-w-txpublic-info@usgs.gov

Figure 4. Dissolved oxygen concentrations in water at the USGS 

real-time water-quality monitoring station 295554095093401, Lake 

Houston near Mouth of Jack’s Ditch, June 2–16, 2007.

2 4 6 8 10 12 14 16

0

-5

-10

-15

2

4

6

8

10

12

JUNE 2007

DEPTH BELOW LAKE 

SURFACE, IN FEET

DISSOLVED OXYGEN 

CONCENTRATION, IN 

MILLIGRAMS PER LITER

Figure 2. Lake Houston watershed and water-quality monitoring 

stations near Houston, Texas.

Houston

# #

#

##

2 1

3

4

5

LAKE

HOUSTON

Spring Creek

East Fork

San Jacinto River

0 2 10 0 30 40 MILES

30°30'

30°00'

95°30'

95°00'

Site Name

1

2

3

4

5

Spring Creek near Spring, Texas

East Fork San Jacinto River near New Caney, Texas

Lake Houston at CWA Structure near Houston, Texas

Lake Houston at Mouth of Jack's Ditch near Houston, Texas

Lake Houston South of Union Pacific RR Bridge near Houston, Texas

EXPLANATION

Water-quality monitoring

station

#

TEXAS

Study

area

Houston

Figure 3. Increase in turbidity measured at the two tributary 

monitoring stations from October 2006 storm in Lake Houston 

watershed and response of turbidity at site 295554095093401, Lake 

Houston near Mouth of Jack’s Ditch.

500

450

400

350

300

250

200

150

100

50

0

9 11 13 15 17 19 21 23 25

OCTOBER 2006

TURBIDITY, IN FORMAZIN NEPHELOMETRIC UNITS

08068500 Spring Creek near Spring, Texas

08070200 East Fork San Jacinto River near

New Caney, Texas

295554095093401 Lake Houston at Mouth 

of Jack’s Ditch near Houston, Texas