Blackwater National Wildlife Refuge

Site Description

  • State: Maryland
  • County: Dorchester
  • Ownership: Federal


  • 13 impoundments: 351 total acres

Ecology and Management

Blackwater National Wildlife Refuge has the largest breeding population of American Bald Eagles north of Florida. Photo by Alan Cressler.

The thirteen impoundments within the Blackwater National Wildlife Refuge are renowned for their abundance and diversity of waterfowl and wading bird species. Additionally, Blackwater National Wildlife Refuge is home to the largest breeding population of American Bald Eagles north of Florida and has been named a Wetland of International Importance. Observations by refuge staff and ornithologists have identified 281 bird species that regularly use the entire refuge complex. Along Wildlife Drive, which forms the bayside barrier for many of the impoundments, 242 bird species have been reported to eBird.org, including impressive high counts of and waterfowl. For example, highs of 15,000 Canada Geese; 12,000 Snow Geese; 1,150 Tundra Swans and 692 Common Merganser were seen from Wildlife Drive since 2010. The Friends of Blackwater National Wildlife Refuge report that upwards of 35,000 geese and 15,000 ducks can be seen during the November migration. Waterbird use of the impoundments is monitored through the Integrated Waterbird Management and Monitoring Program (IWMM).

The impoundments are subject to moist soil management. Pool drawdowns typically occur between mid-March and early June, depending on the wildlife objectives and moist soil plant/invertebrate response desired. Drawdown is initiated in most pools first by gravity flow, but pumping is often required in most of the impoundments to remove all the water. Several permanent and seasonal pumping stations, utilizing gasoline, diesel, and electric pumps, are operated and maintained. Rates of drawdown are critical, and, depending on the pool bottom topography and soil type or organic content, can occur rapidly or must be prolonged. All drawdowns are completed by mid-June, and pool bottoms are maintained as moist as weather conditions will allow to facilitate the germination, growth, and production of a wide diversity of emergent moist soil plants.


The impoundments at Blackwater National Wildlife Refuge are sheltered by around 9,000 acres of brackish marsh. However, between 1938 and 2006 marsh was lost at a rate of 74 acres per year (Lerner et al. 2013). As this rate increases with the rate of sea-level rise over the next century the habitat within the impoundments will become increasingly valuable to birds which use the refuge. Despite their proximity to open water, the impoundments have not historical records of damage.

Human Value

Blackwater NWR received 82,163 visitors in 2011. The refuge also hosts a Youth Conservation Corps program in the summer, as well as providing educational opportunities to 1,700 students and scouts on an annual basis. Despite its rural location Blackwater NWR is one of the most popular birding locations in the state of Maryland.

Literature Resources

Below is a list of articles describing research occurring at or near the impoundments:
  • Beyer, W. N., D. Day, A. Morton, and Y. Pachepsky. 1998. Relation of lead exposure to sediment ingestion in mute swans on the Chesapeake Bay, USA. Environmental toxicology and chemistry 17:2298-2301.
  • Carowan, G. A. Chesapeake Marshlands National Wildlife Refuge Complex Comprehensive Conservation Plan. Washington, D. C.: U. S. Fish and Wildlife Service; 2006.
  • Green, A., J. Lyons, M. Runge, W. Kendall, H. Laskowski, S. Lor, and S. Guiteras. Timing of impoundment drawdowns and impact on waterbird, invertebrate, and vegetation communities within managed wetlands, Study manual – Final version field season 2007. Laurel, Maryland: USGS Patuxent Wildlife Research Center; 2007.
  • Green, A. W., W. L. Kendall, H. P. Laskowski, J. E. Lyons, L. Socheata, and M. C. Runge. Draft version of the USFWS R3/R5 Regional Impoundment Study. Washington, D. C.: U. S. Fish and Wildlife Service; 2008.
  • Jensen, M. N. 2003. Coming of age at 100: Renewing the National Wildlife Refuge System. Bioscience 53:321-327.
  • Larsen, C., I. Clark, G. Guntenspergen, D. Cahoon, V. Caruso, C. Hupp, and T. Yanosky. The Blackwater NWR Inundation Model: Rising Sea Level on a Low-lying Coast—Land Use Planning for Wetlands. Reston, Virginia: U.S. Geological Survey; 2004. Report nr 04–1302.