Marin Municipal Water District this week began looking into amending its state and federal requirements for creek releases—part of a plan to feed thirsty customers from two reservoirs, one of which is reserved for emergencies. But the prospect of diminished releases into Walker and Lagunitas Creeks has some concerned about endangered coho salmon that typically spawn there.

The district cannot take action without the approval of the State Water Resources Control Board and the California Department of Fish and Wildlife, said Greg Andrews, the district’s fishery program manager. They are also consulting with the National Marine Fisheries Service and U.S. Fish and Wildlife. Modification of the releases from Soulajule Reservoir, an emergency reservoir that is currently about half full, would likely happen by March 1. Modifications to Kent Lake, which feeds Lagunitas Creek, would not start before March 7.

“I just don’t know what scenario we’ll see play out. Nothing good is happening with this drought,” Mr. Andrews said.

Walker Creek, which empties into Tomales Bay south of Tomales, is currently receiving 12 cubic feet of water a second from Soulajule to keep it flowing. The creek has also seen over 140 juvenile coho this fall and winter, the first run since 2008. Those fish have benefited from over $1 million in streambed restoration funded by the Marin Resource Conservation District, and local ranches have also fenced their herds and restored vegetation along the stream banks. Mr. Andrews said the district is hoping to ensure that future releases enable the smolts to migrate back to the ocean, a journey that typically takes place in March and April but can extend into July.

“That’s sort of the next critical life phase we’re looking at,” Mr. Andrews said. Without enough creek flow, fish can become trapped in isolated pools, with no way to reach the ocean.

Despite the appearance of so many juveniles, the district has not seen any spawning in Walker Creek this year, though the agency does not survey the entire creek.

“We haven’t had rain event that would typically be what would [give fish] the signal or cue to swim upstream to spawn,” Mr. Andrews said.