Passage Conditions and Counts of Fish 

 at the Snake Island Fishway, 

 Little Falls Dam, Potomac River, Md., 

 1960-63 



By 



PAUL R. NICHOLS, Fishery Biologist 



Bureau of Commercial Fisheries Biological Laboratory 

 Beaufort, N.C. 28516 i 



ABSTRACT 



Resident fish such as sucker, carp, channel catfish, bluegill, and black crappie 

 travelled through the fishway, but apparently no anadromous fish ascended the 

 river far enough to reach the fishway. It is possible that: (1) the runs of anadromous 

 fish are now at such a low level that the spawning area above Little Falls is not 

 needed as in former years; (2) the stocks with the instinct to move above Little 

 Falls which were blocked from their natural spawning ground when the Little Falls 

 Dam was rebuilt in 1949 have since disappeared; and (3) the rapids between Chain 

 Bridge and the fishway nnay deter the upstream progress of nnigrating fish. 



Success in reestablishing runs of anadromous fish above Little Falls may re- 

 quire the planting of fertilized eggs and adult fish in the upper river and the con- 

 struction of fish-passage facilities at the rapids above Chain Bridge. Successful 

 hatching of shad eggs and the collection of young shad above Little Falls indicate 

 that the river is suitable for the restoration of this species. 



INTRODUCTION 



The Potomac River originates on the bound- 

 ary between West Virginia and Maryland and 

 flows 290 miles southeasterly before it empties 

 into Chesapeake Bay. Fluvial characteristics 

 disappear at Washington, D.C., the head of 

 navigation. Below Washington, the river is 

 broad and sluggish, forming one of the largest 

 estuaries on the Atlantic Coast. 



Between Washington and Great Falls, which 

 is 15 miles upstream and has always been a 

 barrier to the upstream movement of fish, 

 the river passes over the "fall line." This 

 area has numerous shoals and several sn-iall 

 falls. The river channel becomes constricted 

 about 5 miles above Washington, at which 

 point is an outcropping of bedrock at Little 

 Falls (fig. 1). 



Among the most valuable fish of the Potomac 

 River are those that spend most of their 

 lives in salt or brackish water, but require 

 fresh water for spawning and nursery grounds. 

 They include American shad, Alosa sapidis- 

 sima; hickory shad, A^. mediocris ; alewife, A^. 

 pseudoharengus; blueback herring, A. aesti- 



■■■ Present address: Bureau of Commercial Fisheries, 

 Washington, D.C. 20240. 



valis ; striped bass, Roccus saxatilis ; and white 

 perch, R^. americanus . Large numbers of these 

 fish move up the Potomac each spring toward 

 their natural spawning grounds. Before 1942 

 some fish moved upstream as far as Great 

 Falls, particularly when a dam at Little Falls, 

 constructed in 1831, contained breaks from ice 

 damage during the preceding winter. The 

 Little Falls Dam was rebuilt in 1943-49; 

 after completion it obstructed the upstream 

 movement of fish beyond this point. 



Because the reconstructed Little Falls Dam 

 blocked the upstream movement of fish, the 

 conservation agencies of Maryland and 

 Virginia, together with the Fish and Wildlife 

 Service, began to explore means whereby the 

 10-mile area between Little Falls and Great 

 Falls could again be used by anadromous fish. 

 An additional complication was the plan of 

 the U.S. Army Corps of Engineers to con- 

 struct a new dam at Little Falls upstream 

 from the old dam. The new structure was to 

 be a concrete overflow 9-foot-high dam, de- 

 signed to maintain a pool from which the Dis- 

 trict of Columbia could draw additional water. 

 Efforts by the conservation agencies to get 

 fish passage facilities at Little Falls were 

 successful; the new dam, including the Snake 

 Island fishway, was completed in the fall of 1959. 



