Success Stories: Cow Bridge Branch

Stockley Branch flows into Cow Bridge Branch watershed, which spans 28,676 acres and is located in the Indian River watershed in southeastern Sussex County. The Indian River Bay watershed makes up one of three of Delaware’s interconnected Inland Bays (Rehoboth Bay, Indian River Bay, and Little Assawoman Bay).


Runoff from agricultural and residential areas caused high bacteria levels in Delaware’s Stockley Branch. As a result, DNREC added Stockley Branch to the 303(d) List for bacteria. Watershed stakeholders provided technical assistance and installed agricultural BMPs in the watershed, causing bacteria levels to decline in the stream. As a result, DNREC removed the Stockley Branch from the state’s 2008 list of impaired waters for bacteria.


Monitoring data collected in the late 1990s indicated that Stockley Branch failed to meet the state’s Enterococcus bacteria numeric criterion, which requires the annual geometric mean to be less than 100 colony-forming units per 100 milliliters. Stockley Branch did not support its freshwater primary contact designated use, prompting the state to add it to Delaware’s 303(d) List for bacteria and nutrients.

In 1998 and 2006, the EPA developed TMDLs to address the nutrients and bacteria loading, respectively, throughout the Indian River watershed. The 1998 TMDL required an 85% reduction in nitrogen and a 65% reduction in phosphorus loadings. The 2006 TMDL required that the overall bacteria loading be reduced by 42% from the 2000–2005 baseline levels in freshwater regions of the Inland Bays drainage basin, which includes the Indian River basin.

Primary sources of NPS pollution in the watershed likely include runoff from agricultural activities (e.g., fertilizer and manure application), concentrated areas of animal production, and urban activities.


The Sussex Conservation District offered technical assistance to the farming community by providing nutrient management planning and cost-share funding for agricultural BMPs.

  • Natural Resources Conservation Service conservation plans and Environmental Quality Incentives Program contracts were developed
  • 11,000 acres enrolled for cover crops over five years
  • Nutrient management plans implemented on approximately 9,228 acres
  • 26 manure storage units installed
  • 11 poultry composters installed
  • 84 heavy use area protection pads installed
  • 7,492 tons of manure transferred outside of the watershed

Conservation Reserve Enhancement Program BMPs:

  • 1.0 acre of grass buffer installed
  • 9 acres of riparian buffers installed
  • 10.2 acres of wetlands restored
  • 17.3 acres of wildlife plantings
  • 219.4 acres of hardwood trees planted

Urban BMPs installed between 2011 and 2016:

  • Retrofit of a dry stormwater pond to a bioretention facility with the use of biochar: 1.6 acres treated
  • Restoration of 1,000 ft. of impaired stream channel: 30 acres treated


Bacteria levels have decreased in response to the more than 10 years of water quality protection and restoration efforts. DNREC collected monitoring data at STORET Station 308281 in Cow Bridge Branch between September 2002 and August 2007. The geometric mean of the 31 samples collected over the 5-year period was 59 colony-forming units per 100 milliliters. This was well below Delaware’s freshwater bacteria water quality standard, so DNREC removed the 8.23 mile segment of Stockley Branch (DE-140-006) from the state’s list of impaired waters in 2008 per its Assessment and Listing Methodology. The Draft 2018 Integrated Report showed that the segment continued to meet the applicable water quality standards for bacteria.

Partners and Funding

  • Center for the Inland Bays
  • Clean Water Act Section 319 funds ~ $1.1 million
  • Conservation Reserve Enhancement Program
  • Delaware Conservation Cost Share Program
  • Delaware Nonpoint Source Program
  • Environmental Quality Incentives Program
  • Natural Resources Conservation Service
  • Sussex Conservation District