Blackwater National Wildlife Refuge
Site Description
- State: Maryland
- County: Dorchester
- Ownership: Federal
Impoundments
- 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 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.
Vulnerability
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
- 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.