Rahway River migrations. Fish ladders are inundated structures with small underwater steps that allow fish to navigate around a dam and continue their migration. Other approaches include removing obstructions that are inoperative or no longer serve their purpose, or improving water quality and reducing debris that obstructs passage. The fish targeted for upstream passage at the Rahway River Water Supply Dam are alewife (Alosa pseudoharengus), blueback herring (Alosa aestivalis), gizzard shad (Dorosoma cepedianum), white perch (Morone Americana) and the endangered American eel (Anguilla rostrate). Alewife and blueback herring are collectively referred to as river herring due to their similarity in appearance, range,
Fish Hook River Fish Hook River is considered to begin in the city of Park Rapids, at a dam forming the Fish Hook River Reservoir, which was constructed to supply hydropower at the site of rapids on the river. From Park Rapids the Fish Hook River flows south-southeastwardly through Todd, Straight River, and Hubbard townships, collecting the Straight River from the west. It flows into the Shell River from the north in Hubbard Township. The Fish Hook River Reservoir flows from Fish Hook Lake, which collects the river's northern watershed. The Portage and Potato rivers flow short distances to the lake from Portage