At Jug Bay the Patuxent River meanders through the most extensive tidal freshwater wetland in Maryland. Although the site is several miles from the coast and has the appearance of a typical inland river the tide here rises and falls more than 2 feet, exposing broad mudflats at low tide. The marshes contain over 50 plant species with wild rice, cat-tail, spatterdock and pickerelweed among the dominants. This IBA extends from the Route 4 bridge near Upper Marlboro to Spice Creek near Lower Marlboro and includes includes portions of three publicly owned conservation areas: Jug Bay Wetlands Sanctuary, owned by Anne Arundel County, Patuxent River Park, owned by M-NCPPC and Merkle Wildlife Sanctuary, owned by Maryland DNR.
The diverse emergent wetland vegetation, including large wild rice beds, hosts one of the greatest concentrations of rails during fall migration anywhere in North America. Surveys have estimated over 4000 Soras present at one time, and 754 Soras and 82 Virginia Rails have been banded here in a single Fall season. The wetlands are also important for breeding Least Bittern, a species listed by Maryland DNR as In Need of Conservation. Winter waterfowl average 12000; the great majority of these are migratory Canada Geese, and Mallard, Black Duck, Pintail, and Green-winged Teal occur in smaller numbers.
Lying just 12 miles from Washington DC in a region that is experiencing great pressure from residential and commercial development, the main conservation threat at Jug Bay is the indirect affects of such development in the watershed. Increased sedimentation and runoff resulting from construction an increasing area of built surfaces will likely impact water quality adversely. Excessive grazing of wild rice by resident Cananda geese caused a decline of the rice beds through the 1990s and this in turn caused numbers of migrant rails to decline greatly. However, management of the resident Canada Goose population has allowed the wild rice to increase again and in 2005 migrant soras were present in large numbers.