St Marys Lake

Located in Baltimore County

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St Marys Lake

Descriptions/characteristics - St Mary’s Lake Park is located in the headwaters of the St Mary’s River in the center of St. Mary’s County, Maryland. It consists of more than 2,000 acres of park land and a 225 acre lake. The property is managed by the Maryland State Park Service and is divided into two areas. Site one includes St. Mary’s Lake and is accessed on Camp Cosoma Road from Maryland Route 5. Site two is located along Indian Bridge Road. The park is a multi-use area for fishing, hiking, mountain biking, bird watching and boating and hunting. Fishermen may fish the waters of the park, but are asked to stay off of the spillway leading down from the dam. This off limits area is posted with signs.

St Mary’s Lake and river are surrounded by a mature hardwood forest mixed with some conifers. The head of the lake is characterized by shallow, marshy terrain that flows into a deeper lake basin containing several shallow coves, points, and shoals.

Water Quality - The water quality of St. Mary’s Lake is of low productivity and has an average pH of about 6. The water is stained with tannins, but clear. PH is not stable in the lake, contributing to the poor productivity of both gamefish and forage fish.

Macrophyte/SAV - Very few aquatic plants were present when the lake was created in 1975. In the early 1990’s some plants were planted in the headwaters and coves to create some habitat for fish and other aquatic life. Spatterdock (Nuphar lutea), a yellow water lily, was able to survive the conditions of the lake and has now been able to populate some shallow areas of the lake in small patches. Low water milfoil (Myriophyllum humile) is the only submerged aquatic plant that has been established since the lake was created. Low water milfoil tends to grow well in lakes having lower pH. Bladderwort does gain a foothold in the lake from time to time, but never becomes permanently established.

Managed Fish Species - The fish population in St. Mary’s Lake is managed by Maryland Department of Natural Resources Freshwater Fisheries and Hatchery Division. Anglers can expect to find largemouth bass, bluegill, redear sunfish, black crappie, chain pickerel, yellow perch, brown bullhead, and a small population of flier in the lake. Golden shiners have annually been stocked in the lake for several years to supplement the forage that is absent from the fish community. The fisheries service has deployed fish attractors in the form of pickle barrel structures in select locations around the lake in 2006. These structures are made of sunken locust and Osage orange tree branches cemented into buckets and were placed in groups of twos and threes at three locations. Concrete reef balls (14) and anchored drainage pipe (6) have also been placed along drop-offs around the lake. During low water conditions, the division has seeded exposed soil to encourage some vegetative cover for fish when water levels return to normal.​

Northern snakehead have migrated their way upstream in the St. Mary’s River from the Potomac and can be pursued in the watershed below the lake spillway. Please honor the No Fishing signs at the outflow of the lake and stay off the spillway.

Access/Restrictions - A 7.5 mile trail circles the lake providing extensive shoreline access for fishing. A boat ramp is available , but boaters are restricted to electric motors only. A protected Slot Length Limit is in effect for large and smallmouth bass.

Recent Surveys - St Marys Lake was last surveyed in 2018. Largemouth bass were found to be very abundant with a desirable proportion of quality size fish present. Largemouth bass were considered to be in good physical condition.

St Marys Lake Largemouth Bass Population Metrics from 2018 Surveys at Four Sites.
Number of fish observed during study
Population Size Distribution (PSD)
Fish per hour greater than 8 inches
Fish per hour greater than 12 inches
Average Relative Weight

St Marys Lake Black Crappie Population Metrics from the 2018 Surveys at Four Sites.
Number of fish observed during study
Population Size Distribution (PSD)
Fish per hour greater than 8 inches
Fish per hour greater than 9.8 inches