Jeremy Johnson

Russ Frydenborg

Florida Department of Environmental Protection

Division of Environmental Assessment and 

Restoration
Loxahatchee Estuary
The Loxahatchee Estuary

Geographical and Physical Description

 The Loxahatchee estuary includes the marine, polyhaline and 

meso/oligohaline portions of the Loxahatchee River between the river and where it meets the Atlantic at Jupiter Inlet 

 The watershed for the estuary includes areas in northeastern 

Palm Beach County and southeastern Martin County, and major 

cities and towns in the watershed include Jupiter, Tequesta, Juno 

Beach, Jupiter Island, Jupiter Inlet Colony, Jupiter Farms, Hobe 

Sound, and Palm Beach Gardens

 The Loxahatchee River is classified as Class II (shellfish 

harvesting) and has been designated as an Outstanding Florida 

Water (OFW).
Physical Characteristic Values Source 

Estuarine surface area (km2) 988 acres Loxahatchee River Environmental 

Control District

Mean depth (m) 1-3 ft. Loxahatchee River Environmental 

Control District

Temperature 14° C-32° C Loxahatchee River Environmental 

Control District

Salinity Range: 0-33 PSU Loxahatchee River Environmental 

Control District

Residence Time < 1 day

Mixed Semi-Diurnal Tide

60% of Freshwater is flushed at 

each tide 

Loxahatchee River Environmental 

Control District
Loxahatchee Estuary

Land Use

Acres Percent Description

31077 21.10% Urban

17605 11.95% Ag

5786 3.93% Shrub/Brushland

26614 18.07% Forested

11345 7.70% Open Water

51315 34.84% Wetland

743 0.50% Beaches/Disturbed 

2796 1.90% Utilities
Response 

variable 

Observed 

historically?

Observed 

currently? 

Explanation Source

Low DO (hypoxia/anoxia) No No Currently, DO is 

considered to be high in 

the estuary and is meeting 

the Class III requirements.

Loxahatchee River 

Environmental Control 

District

Reduced clarity No No None have been reported 

but continued monitoring 

is warranted.

Loxahatchee River 

Environmental Control 

District

Increased chlorophyll a 

concentrations

No Yes A slight increase in the 

“polyhaline” portion of 

the Loxahatchee has been 

reported, which can be 

attributed to the 

hydrological modification. 

Loxahatchee River 

Environmental Control 

District

Phytoplankton blooms 

(nuisance or toxic)

No No No phytoplankton blooms 

have been reported for 

the system.
Response 

variable 

Observed 

historically?

Observed 

currently? 

Explanation Source

Problematic epiphyte 

growth 

No No No problematic epiphyte 

growth has been reported 

for the system.

Problematic macroalgal 

growth

No No No problematic 

macroalgal growth has 

been reported for the 

system.

SAV community changes 

or loss

No No SAV continues to increase 

in the area and is not 

cause for concern.

Loxahatchee River 

Environmental Control 

District

Emergent vegetation 

community changes or 

loss 

Yes Yes The altered salinity of the 

Loxahatchee Estuary has 

allowed estuarine plants 

to out compete fresh 

water trees that once 

lined the river banks. As 

the saltwater intruded the 

soils, many trees were 

Loxahatchee River 

Environmental Control 

District
Response 

Variable

Observed 

Historically?

Observed 

Currently?

Explanation Source

Coral/Hardbottom

community 

changes or loss

N/A N/A N/A

Impacts to Benthic 

Community

No No None reported, 

although not 

well studied

Fish Kills No No No fish kills 

have been 

reported in the 

system
Factors Observed? Explanation Source

Increased nutrient loading 

or concentrations from 

historical levels

No None that have been observed. Loxahatchee 

River 

Environmental 

Control District

Mitigating factors that 

could prevent nutrient 

expression

No None that have been observed. Loxahatchee 

River 

Environmental 

Control District

Other significant stressors 

to biological communities

Yes Salinity Issues attributed to flow 

reductions and the dredged inlet.

Loxahatchee 

River 

Environmental 

Control District

Natural episodic events 

contributing to nutrient 

regime (e.g., seasonal or 

hydrologically driven)

Yes Hurricanes and other storms have 

impacts. 

Loxahatchee 

River 

Environmental 

Control District
The Loxahatchee Estuary

Biological Summary

 Seagrass Communities

 Seagrass beds in the estuary are dominated by Johnson’s 

Seagrass Halophila johnsonii, Shoal Grass Halodule

wrightii, Paddle Grass Halophila decipiens, and Manatee 

Grass Syringodium filiforme

 The increase in the distribution of SAV in the 

Loxahatchee from 1998 to 2007 has been 

extraordinary. 

 This increase has been attributed to the ongoing 

hyrdologic restoration efforts in the Loxahatchee 

basin. 
The Loxahatchee Estuary

Biological Summary

1998 SAV coverage in the 

Loxahatchee estuary. 2007 SAV Coverage
The Loxahatchee Estuary

Biological Summary cont.

 Oysters

 Two species of oyster were observed in the estuary of the 

Loxahatchee River, the American or Eastern Oyster, 

Crassostrea virginica, and the Flat Oyster, Isognomon

alatus

 The data collected from the sampling points indicate 

that the greatest number of beds, the largest spatial 

distribution, and the highest densities were recorded in 

the Northwest Fork.
The Loxahatchee Estuary

Biological Summary

 The Loxahatchee Estuary is fully meeting its designated uses of 

“Recreation, Propagation and Maintenance of a Healthy, Well- balanced Population of Fish and Wildlife” based on the 

following information:

 The most sensitive biological endpoint in the Loxahatchee Estuary 

is seagrass, and the seagrass habitat is healthy and actually expanding in coverage. 

 The seagrass beds are large, diverse and continuing to grow after the destructive 2004 Hurricane season

 Fish and invertebrate data show high abundances in seagrass beds 
The Loxahatchee Estuary

Sources of Nutrients

 Loxahatchee River

Wetlands/leaf litter

 Stormwater Runoff

Atmospheric Deposition
Water Quality Studies

Mean Annual TN

TN in the Loxahatchee from 1998 to 2009.
Water Quality Studies

Mean Annual TP

TP in the Loxahatchee from 1998 to 2009.
Water Quality Studies

Mean Chl-a

Chl-a in the Loxahatchee from 1998 to 2009.
Proposed numeric nutrient criteria for

Total Nitrogen in the Loxahatchee Estuary 

(mg/L)

Proposed Criteria

Marine Polyhaline Meso/Oligohaline

Existing Long Term 

Geometric Mean 0.62 0.97 1.16

Maximum Allowed 

Long Term Geometric 

Mean 0.68 1.07 1.28

Annual Geometric 

Mean for the Network 

of Stations (2 of 5 year 

exceedance rate) 1.11 1.48 1.54

Annual Geometric 

Mean for a Single Site 

(2 of 5 year 

exceedance rate) 1.19 1.56 1.59
Proposed numeric nutrient criteria for 

Total Phosphorous in the Loxahatchee 

Estuary (mg/L)

Proposed Criteria

Marine Polyhaline Meso/Oligohaline

Existing Long Term 

Geometric Mean 0.019 0.039 0.067

Maximum Allowed 

Long Term Geometric 

Mean 0.021 0.043 0.074

Annual Geometric 

Mean for the Network 

of Stations (2 of 5 year 

exceedance rate) 0.027 0.052 0.09

Annual Geometric 

Mean for a Single Site 

(2 of 5 year 

exceedance rate) 0.03 0.059 0.107
Proposed numeric nutrient criteria for 

Chl-a in the Loxahatchee Estuary

(ug/L)

Proposed Criteria

Marine Polyhaline Meso/Oligohaline

Existing Long Term 

Geometric Mean 2.9 7.9 5.1

Maximum Allowed 

Long Term Geometric 

Mean 3.2 8.7 5.6

Annual Geometric 

Mean for the Network 

of Stations (2 of 5 year 

exceedance rate) 4.2 11.4 7.0

Annual Geometric 

Mean for a Single Site 

(2 of 5 year 

exceedance rate) 5.1 13.0 7.5
The Loxahatchee Estuary

What’s next?

• Provide additional comments on estuary report to 

Jeremy Johnson

• Phone: 850-245-8129

• Email: Jeremy.K.Johnson@dep.state.fl.us

• Finalize estuary reports.