Columbia, feeding activities of increasing 
numbers of the introduced European carp, 
and greater pollution of the river by domestic 
sewage from Washington, D.C., andits suburbs. 
According to observations made by F, M, Uhler, 
the increased domestic sewage in the river 
promoted a vigorous growth of blue-green 
algae, which decomposed and released poison- 
ous substances that damaged many aquatic 
vascular plants. Furthermore, the prolonged 
unprecedented drouthfrom 1930 to 1932 brought 
slightly brackish estuarine waters upthe river 
to the mouth of Occoquan Bay. During the 
Same period, the introduced waterchestnut 
became more and more abundant in many areas 
and effectively crowded out many of the more 
desirable native aquatic plants (Gwathmey, 
1945). As a result of these various changes, 
the greater part of the submerged vegetation 
of the upper Potomac estuary gradually dis- 
appeared during the period 1930-35. 
At present, the portion of the Potomac 
River estuary downstream from the District 
of Columbia to Chicamuxen Creek (Charles 
County, Maryland) has no submerged vascular 
plants. Fairly extensive beds of submerged 
vegetation still occur in the fresh estuarine 
waters between Chicamuxen Creek and Mary- 
land Point. Even these waters, however, are 
moderately turbid, so vegetation is restricted 
to narrow, shallow zones along the shores. 
The principal native plants are wildcelery, 
southern naiad, claspingleaf pondweed, and 
common waterweed. The introduced Eurasian 
watermilfoil recently has invaded this area 
and rapidly is becoming a serious pest. 
Fishes 
Some of the more common species offresh- 
water fish include the yellow perch (Perca 
flavescens), chain pickerel (Esoz niger), lar ge- 
mouth blackbass (Micropterus salmoides), crappie 
(Pomozis sp.), pumpkinseed sunfish (Lepomis 
gibbosus), and bullhead (lectalurus nebulosus). 
Certain brackish or saltwater fish often are 
abundant during spawning periods. These in- 
clude the striped bass (Roccus sazetilis), white 
perch (Roccus americanus), white shad (Alosa 
sapidissima), hickory shad (Pomolabus mediocris), 
and alewife herring (Pomolobus pseudoharengus). 
Invertebrates 
Pelecypod and gastropod mollusks and aqua- 
tic insects are the predominant invertebrates. 
Some of the characteristic species of inver- 
tebrates are: 
Pelecypod (bivalve) Mollusks 
Elliptio complanatus 
Anodonta sp. . 
Sphaerium sp. 
Pisidium sp. 
Gastropod ({univalve) Mollusks 
Physa sp. 
Gyraulus sp. 
Valvata tricarinata 
Amnicola limosa 
Gillia altilis 
Ozytrema virginica 
Cladocera 
Daphnia sp. 
Amphipod Crustaceans 
Gammarus tigrinus 
Crangonyz sp. 
Water Mites 
Hydrachnellae : 
Insects 
Mayfly Nymphs (Ephemeroptera) 
Dragonfly Nymphs (Anisoptera) 
Water Boatmen (Corixidae) 
Alderfly larvae (Sialidae) 
Caddisfly larvae (Trichoptera) 
Midge larvae (Chironomidae) 
Waterfowl 
During spring and fall, often one-fourth or 
more of the Upper Chesapeake migrant water- 
fowl are on the fresh estuarine bays. During 
winter, less than 10% use this habitat. 
Characteristic species of transient water- 
fowl are: 
Primary Species 
Canvasback 
Lesser Scaup 
American Coot 
Whistling Swan 
Canada Goose (local) 
American Widgeon 
Redhead 
Secondary Species 
Mallard Common Goldeneye 
Black Duck Bufflehead 
Pintail Ruddy Duck 
Ring-necked Duck Common Merganser 
Other species that occur in small numbers 
include the Gadwall, Green-winged Teal, Blue- 
winged Teal, Greater Scaup, Oldsquaw, and 
Red-breasted Merganser. 
Areas that still contain extensive beds of 
submerged aquatic plants are favored habitats 
for migrant populations of Canvasbacks and 
other diving ducks, American Widgeons, 
Whistling Swans, and American Coots. Areas 
along the Sassafras and Bohemia Rivers that 
adjoin extensive agricultural lands attract 
large numbers of Canada Geese and fair 
numbers of Mallards and Black Ducks. Winter- 
ing populations ordinarily are relatively small 
and vary. considerably from year to year, 
depending on ice conditions. 
