Caution
Rating icon - Chlorophyll a Rating icon - Total Nitrogen Rating icon - Total Phosphorous Rating icon - Dissolved Oxygen Saturation

3 out of 4 primary indicators were rated as PASS.

"Primary" are nutrient related (Chl, N, P) and bacteria (B) parameters.

All four indicators must pass for the creek to be rated as PASS.

Greyed out values indicate no data for the report year.

  • Size: 47,518 acres
  • Location: North and central Sarasota County, south Manatee County
  • Discharges into: Dona Bay

For more information, please see: Cow Pen Slough Basin Master Plan (USDA Report, 1997)

View county-wide water quality trends »

Cow Pen Slough

Water Chemistry Ratings

Monitoring data is analyzed to determine stream health based on State water quality standards. Official determination of impairment or attainment of the water quality standards is performed by FDEP and is based on at least three years and up to seven and a half years of data. Information on approximately 17 different parameters are collected at stream sites, but only total nitrogen, total phosphorus, chlorophyll a, dissolved oxygen (percent saturation), and bacteria are assessed according to established water quality criteria mandated by the Clean Water Act. Additionally, the floral and faunal communities (SCI) are assessed at some sites to determine whether waters support a healthy aquatic community.

The "pass/fail" conditions presented here do not indicate impairment as determined by the official Florida Department of Environmental Protection Impaired Waters Rule assessment but, rather, give an indication of stream condition in a particular year in relation to the set regulatory numeric limits. Streams receive an annual "PASS" rating for each parameter if the mean value is below the regulatory value and a "FAIL" rating if the mean value exceeds the regulatory value. Not all water quality parameters have an established numeric criterion, so only some of the graphs below show the regulatory limit, represented by a horizontal red line.

Chart Legend
  • Monthly Average
  • Threshold
  • Annual Mean

The graphs here illustrate results over the past five years. Data from sites monitored within a single waterbody identification basin (WBID) are combined to determine water quality status for each WBID, and the annual geometric mean of sample results is indicated on the graph for the most recent year. The table to the left of the graph gives the annual and historic range of values for the indicator.

Click the graph to view a larger image and to download the full dataset.

Freshwater Portion of the Creek

Data for the following WBIDs is averaged when compiling the data below:
  • 1924
  • 1924B
  • 1987
  • 1994
  • 1994A
  • 1996
  • 2004

Chlorophyll a

Units: µg/l Year
2025
Historical
period of record
High 191.00 312.00
Mean 16.5409 10.8201 29.23829
Low 1.00 0.314
No. of Samples 88 1,290
  • Monthly Average
  • NNC 20.00 µg/l
  • Annual Mean

Nitrogen, Total

Units: mg/L Year
2025
Historical
period of record
High 2.017 3.695
Mean 1.0309 1.1671 0.42310833
Low 0.035 0.035
No. of Samples 70 1,041
  • Monthly Average
  • NNC 1.65 mg/L
  • Annual Mean

Phosphorus, Total

Units: mg/L Year
2025
Historical
period of record
High 0.452 1.19
Mean 0.139 0.1316 0.15741919
Low 0.029 0.008
No. of Samples 70 1,147
  • Monthly Average
  • NNC 0.49 mg/L
  • Annual Mean

Dissolved Oxygen Saturation

Note: Dissolved oxygen saturation percentages above the regulatory threshold meet established water quality targets.
Units: percent (%) Year
2025
Historical
period of record
High 146.44 227.16
Mean 56.78 53.22 36.17853
Low 4.47 0.00
No. of Samples 65 1,187
  • Monthly Average
  • NNC 38.00 percent (%)
  • Annual Mean

BOD, Biochemical oxygen demand

Units: mg/l Year
2025
Historical
period of record
High 8.62 11.80
Mean 1.89 1.49 1.38634
Low 1.00 0.00
No. of Samples 65 978
  • Monthly Average
  • Annual Mean

Color

Units: PCU Year
2025
Historical
period of record
High 220.00 650.00
Mean 106.05 110.16 85.29527
Low 37.00 10.00
No. of Samples 65 1,136
  • Monthly Average
  • Annual Mean

Escherichia coli

Units: MPN/100ml Year
2025
Historical
period of record
High 2755.00 2755.00
Mean 19.72 21.01 177.81111
Low 4.10 1.00
No. of Samples 68 691
  • Monthly Average
  • Annual Mean

Nitrogen, Ammonia + Ammonium as N

Units: mg/L Year
2025
Historical
period of record
High 0.78 0.812
Mean 0.03 0.01 0.07822282
Low 0.003 0.00
No. of Samples 70 1,109
  • Monthly Average
  • Annual Mean

Nitrogen, Kjeldahl

Units: mg/L Year
2025
Historical
period of record
High 1.99 8.40
Mean 1.06 1.12 0.44438895
Low 0.47 0.00
No. of Samples 70 1,143
  • Monthly Average
  • Annual Mean

Nitrogen, Nitrite + Nitrate as N

Units: mg/L Year
2025
Historical
period of record
High 0.29 1.36
Mean 0.02 0.02 0.08306426
Low 0.004 0.00
No. of Samples 69 995
  • Monthly Average
  • Annual Mean

pH

Units: None Year
2025
Historical
period of record
High 8.27 11.50
Mean 7.44 7.56 0.41602
Low 6.59 5.70
No. of Samples 65 4,524
  • Monthly Average
  • Annual Mean

Salinity

Units: PSS Year
2025
Historical
period of record
High 0.56 76.50
Mean 0.2 11.24 18.20995
Low 0.09 0.00
No. of Samples 61 4,088
  • Monthly Average
  • Annual Mean

Specific conductance

Units: µmho Year
2025
Historical
period of record
High 1118.61 59844.40
Mean 438.85 10288.05 20860.4872
Low 187.41 0.10
No. of Samples 74 4,479
  • Monthly Average
  • Annual Mean

Temperature, water

Units: °F Year
2025
Historical
period of record
High 196.8116 348.7984
Mean 9.29 78.33 32.58068
Low 0.00 0.00
No. of Samples 185 4,382
  • Monthly Average
  • Annual Mean

Turbidity

Units: NTU Year
2025
Historical
period of record
High 4.20 48.00
Mean 1.8 2.72 3.83116
Low 0.94 0.08
No. of Samples 8 589
  • Monthly Average
  • Annual Mean
Other Measures of Creek Health:

Tidal Portion of the Creek

Data for the following WBIDs is averaged when compiling the data below:
  • 1924A
  • 1994B
Pass

Chlorophyll a

Score: Pass
Units: µg/l Year
2025
Historical
period of record
High 28.6 159.0
Mean 10.0575 8.1939 11.65387
Low 3.56 0.568
No. of Samples 12 346
  • Monthly Average
  • NNC 11.00 ug/l
  • Annual Mean
Pass

Nitrogen, Total

No trend was observed after performing a trend analysis.
Score: Pass
Units: mg/L Year
2025
Historical
period of record
High 1.6 2.2
Mean 1.1433 0.8729 0.38706623
Low 0.894 0.16
No. of Samples 12 278
  • Monthly Average
  • Annual Mean
Pass

Phosphorus, Total

Trend analysis shows a weak decreasing trend.
Score: Pass
Units: mg/L Year
2025
Historical
period of record
High 0.3 0.8
Mean 0.1308 0.1553 0.09769701
Low 0.071 0.026
No. of Samples 11 352
  • Monthly Average
  • Annual Mean
Caution

Dissolved Oxygen Saturation

Note: Dissolved oxygen saturation percentages above the regulatory threshold meet established water quality targets.
Score: Caution
Units: percent (%) Year
2025
Historical
period of record
High 75.1 159.3
Mean 50.94 61.98 23.14652
Low 22.72 1.80
No. of Samples 12 407
  • Monthly Average
  • NNC 56.00 percent (%)
  • Annual Mean

BOD, Biochemical oxygen demand

Units: mg/l Year
2025
Historical
period of record
High 3.6 13.9
Mean 1.6 1.6 1.30173
Low 1.00 0.50
No. of Samples 12 315
  • Monthly Average
  • Annual Mean

Color

Units: PCU Year
2025
Historical
period of record
High 160.0 500.0
Mean 126.48 72.63 72.33466
Low 100.00 5.00
No. of Samples 12 400
  • Monthly Average
  • Annual Mean

Enterococcus Group Bacteria

Units: MPN/100ml Year
2025
Historical
period of record
High 3,076.0 8,200.0
Mean 213.33 274.98 1330.67552
Low 31.00 10.00
No. of Samples 12 166
  • Monthly Average
  • Annual Mean

Nitrogen, Ammonia + Ammonium as N

Units: mg/L Year
2025
Historical
period of record
High 0.2 0.9
Mean 0.09 0.02 0.13263139
Low 0.032 0.00
No. of Samples 12 398
  • Monthly Average
  • Annual Mean

Nitrogen, Kjeldahl

Units: mg/L Year
2025
Historical
period of record
High 1.6 2.2
Mean 1.12 0.86 0.37610197
Low 0.872 0.05
No. of Samples 12 392
  • Monthly Average
  • Annual Mean

Nitrogen, Nitrite + Nitrate as N

Units: mg/L Year
2025
Historical
period of record
High 0.0 0.3
Mean 0.02 0.03 0.04306664
Low 0.009 0.00
No. of Samples 12 332
  • Monthly Average
  • Annual Mean

pH

Units: None Year
2025
Historical
period of record
High 7.5 22.3
Mean 6.95 7.42 0.78824
Low 6.57 5.44
No. of Samples 12 485
  • Monthly Average
  • Annual Mean

Salinity

Units: PSS Year
2025
Historical
period of record
High 40.2 40.2
Mean 14.94 8.65 11.67268
Low 0.39 0.00
No. of Samples 12 365
  • Monthly Average
  • Annual Mean

Specific conductance

Units: µmho Year
2025
Historical
period of record
High 59,038.3 59,038.3
Mean 23866.05 16305.6 17842.593
Low 795.87 20.209
No. of Samples 12 3,390
  • Monthly Average
  • Annual Mean

Temperature, water

Units: °F Year
2025
Historical
period of record
High 195.7 211.6
Mean 175.75 80.54 16.08995
Low 154.2056 51.224
No. of Samples 12 3,293
  • Monthly Average
  • Annual Mean

Turbidity

Units: NTU Year
2025
Historical
period of record
High 11.2
Mean 3.12 1.53947
Low 1.00
No. of Samples 0 318
  • Monthly Average
  • Annual Mean
Other Measures of Creek Health:

Oysters

Because they are immobile and will tolerate a fairly wide salinity range, eastern oysters (Crassostrea virginica) are valuable as an indicator of the relative health of aquatic ecosystems in the tidally-influenced portions of coastal creeks. Sarasota County has established an oyster monitoring program to track the location, types, and status of oyster reefs. Data from this monitoring program is shown below. Learn more about Oysters »

Loading oyster site map...
Most Recent Sarasota County Oyster Monitoring Program Data
Icon Site ID Year Dead Live Total % Live
1 SKC4 2025 40 163 203 80

Impervious Features

Cow Pen Slough is located within the Sarasota Bay Watershed. View details about the Sarasota Bay Watershed »

Rain that falls on land that is in a natural state is absorbed and filtered by soils and vegetation as it makes it way into underground aquifers. However, in developed areas, "impervious surfaces" impede this process and contribute to polluted urban runoff entering surface waters. These surfaces include human infrastructure like roads, sidewalks, driveways and parking lots that are covered by impenetrable materials such as asphalt, concrete, brick and stone, as well as buildings and other permanent structures. Soils that have been disturbed and compacted by urban development are often impervious as well. Learn more about Impervious Features »

The Sarasota County Stormwater Environmental Utility (SEU) mapped impervious surfaces in the County in 2013. A map showing impervious surfaces can be viewed using the Water Atlas Map Viewer tool.

2% of the land area within the Cow Pen Slough Basin is covered by impervious surfaces

Impervious Surface Coverage by Type

Land Use / Land Cover

Cow Pen Slough is located within the Sarasota Bay Watershed. View details about the Sarasota Bay Watershed »

Land use within a creek's watershed has a major effect on its water quality. In general, less development means better water quality. Land Cover/Land Use classifications categorize land in terms of its observed physical surface characteristics (e.g. upland or wetland), and also reflect the types of activity that are taking place on it (agriculture, urban/built-up, utilities, etc.). Florida uses as its standard a set of statewide classifications which were developed by the Florida Department of Transportation. Learn more about Land Use and Land Cover »

Acreage and Percentage within each Land Use / Land Cover Category for Cow Pen Slough Basin
Land Use Classification 1990 1995 1999 2005 2011 2014 2017 2020 2023 Trend
Urban & Built-up 4,5089.5% 6,03812.7% 8,97518.9% 11,00123.2% 11,73024.7% 11,97425.2% 12,40026.1% 13,13127.6% 14,08629.6% Land Use Trend Sparkline
Agriculture 13,32028% 14,16429.8% 14,11229.7% 14,34730.2% 13,51228.4% 13,22727.8% 13,18427.7% 12,67726.7% 11,85324.9% Land Use Trend Sparkline
Rangeland 7,04114.8% 6,16813% 4,0568.5% 2,4485.2% 2,3074.9% 2,4885.2% 2,0504.3% 1,7573.7% 1,6823.5% Land Use Trend Sparkline
Upland Forests 11,44524.1% 10,05921.2% 8,50317.9% 7,48315.7% 7,37615.5% 7,30915.4% 7,13115% 6,79114.3% 6,58813.9% Land Use Trend Sparkline
Water 8161.7% 1,3452.8% 1,5213.2% 1,6443.5% 1,7633.7% 1,8173.8% 1,9414.1% 1,9764.2% 2,1984.6% Land Use Trend Sparkline
Wetlands 10,03521.1% 9,31019.6% 9,36719.7% 9,47119.9% 9,50720% 9,39719.8% 9,44119.9% 9,82620.7% 9,71620.4% Land Use Trend Sparkline
Barren Land 160% 50% 20% 490.1% 1100.2% 770.2% 820.2% 180% 450.1% Land Use Trend Sparkline
Transportation and Utilities 3370.7% 4300.9% 9822.1% 1,0752.3% 1,2132.6% 1,2302.6% 1,2882.7% 1,3422.8% 1,3552.9% Land Use Trend Sparkline
Land Use Chart