The agreed plan, negotiated over two years by FPL and state and federal agencies, would open 40km of water from Bar Mills dam to Hiram dam to migrating fish, over a period of 20 years.

FPL, which owns nine dams on the Saco, would build the fishways on four dams that lack such passages, while building separate passages for eels on all nine dams. The negotiations are linked to the federal relicensing process for FPL’s Bar Mills dam, the first dam that fish migrating upriver cannot pass.

Previously, fish passages were installed at five dams downstream from Bar Mills under a 1994 agreement. The new agreement calls for completing the first fish passage at Bar Mills by 2016. Progressing upstream, the company would build three other passages at three year intervals, with the one at Hiram completed by 2025.

The timetable for creating upstream and downstream passages for American eels at all FPL dams on the Saco would begin in 2008 with dams closest to the mouth of the river; the work would end at the Hiram dam in 2032. An eel passage is considered less difficult to build than a fish passage, because eels can wriggle over solid surfaces. A typical eel passage consists of a trough lined with artificial turf.