TMDL Progress

The County’s 2022 National Pollutant Discharge Elimination System (NPDES) municipal separate storm sewer system (MS4) permit requires that the County develop local restoration plans to address each U.S. Environmental Protection Agency (EPA)-approved total maximum daily load (TMDL) with a stormwater wasteload allocation. The permit requires progress towards meeting those TMDLs to be reported in the Countywide TMDL Stormwater Implementation Plan Annual Report. A summary of the report progress is below. 

For context, the Chesapeake Bay TMDL is a multi-state TMDL that was established in 2010 for total nitrogen (TN) and total phosphorus (TP), which apply to all watersheds in the County. This TMDL focuses on improving water quality in the Chesapeake Bay, not local streams. Local TMDL restoration plans were developed for TN, TP, and total suspended solids (TSS) for the County portions the Anacostia River; Mattawoman Creek; Piscataway Creek; the Middle and Lower Patuxent River; and Upper Patuxent River and Rocky Gorge Reservoir. To see these local TMDLs, visit the Watersheds and Total Maximum Daily Load (TMDL) within Prince George’s County webpage.

Chesapeake Bay TMDL

Figure 1, Figure 2, and Table 1 present the percentage of the TMDL target that has been met as of the fiscal year 2025 annual report, which reports progress through June 30, 2025. The Mattawoman, Piscataway, and Patuxent Middle Oligohaline segmentsheds achieved the highest percentage of meeting the Chesapeake Bay TMDL target for TN (Figure 1); while the Patuxent Middle Oligohaline, Mattawoman, and Patuxent Upper Tidal Fresh are the top three segmentsheds closest to meeting their TP reduction targets (Figure 2). 

Table 1. Target load reduction percent for the Chesapeake Bay TMDL.

Segmentshed	Percent of Target Achieved (%)
	TN	TP
Anacostia Tidal Fresh DC	10.8	20.5
Anacostia Tidal Fresh MD	44.7	35.7
Mattawoman	75.5	72.5
Patuxent Lower Mesohaline	0.4	0.3
Patuxent Middle Oligohaline	51.3	100.0
Patuxent Upper Tidal Fresh	47.6	51.1
Piscataway	56.2	18.6
Potomac Lower Mesohaline	0.0	0.0
Potomac Upper Tidal Fresh DC	8.3	7.0
Potomac Upper Tidal Fresh MD	11.2	11.4
Western Branch	40.7	44.1

Local TMDLs

Figure 3, Figure 4, Figure 5, and Table 2 present the percentage of the local TMDL target that has been met for TN, TP, and TSSs, respectively. The top three watersheds achieving the highest percentage of their TN local TMDL targets are Mattawoman, Anacostia River - Non-Tidal - Northeast Branch, and Anacostia River - Non-Tidal - Northwest Branch (Figure 3). For their TP local TMDL targets, they are Rocky Gorge, Mattawoman, and Anacostia River - Non-Tidal - Northeast Branch (Figure 4). Finally, Upper Patuxent, Lower Patuxent, and Anacostia River - Non-Tidal - Watts Branch are the top three watersheds in the County that have achieved the highest percent of local TMDL targets for TSS (Figure 5). 

Table 2: Percent of TMDL and load reduction target achieved for the local TMDL progress.

Watershed	Percent of Target Achieved (%)
	TN	TP	TSS
Anacostia River - Non-Tidal - Lower Beaverdam Creek	2.7	7.8	4.7
Anacostia River - Non-Tidal - Northeast Branch	11.2	21.1	24.4
Anacostia River - Non-Tidal - Northwest Branch	10.5	12.7	3.5
Anacostia River - Non-Tidal - Watts Branch	9.2	27.4	56.4
Anacostia River - Tidal	3.0	6.0	5.2
Lower Patuxent	n/a	n/a	100
Mattawoman	14.4	50.4	n/a
Middle Patuxent	n/a	n/a	0.3
Piscataway	n/a	n/a	56.1
Rocky Gorge	n/a	100	n/a
Upper Patuxent	n/a	n/a	100

Notes:

n/a=not applicable. There is not a local TMDL for that specific constituent. 

 

The Anacostia Watershed TMDL reduction progress might seem insignificant; this is due to the large percent reduction (81% nutrients; 85% TSS) required by MDE’s TMDLs (completed in 2008). For more information on the number of restoration practices installed annually see the County’s annual NPDES MS4 report.