Sonoma County could receive millions of dollars toward the cost of restoring coho salmon habitat in Dry Creek, thanks to legislation signed by President Barack Obama on Tuesday.

The relief was a provision of a larger piece of legislation, and would affect a stretch of the creek downstream from Lake Sonoma.

The initial effect is expected to lead to a $5 million contribution from the U.S. Army Corps of Engineers for studies related to the 6-mile Dry Creek restoration project mandated in 2008 by the National Marine Fisheries Service, Sonoma County Water Agency spokeswoman Ann DuBay said.

But the legislation backed by North Bay Reps. Mike Thompson and Jared Huffman, which extends the Army Corps obligations downstream from the Warm Springs Hatchery it operates at Lake Sonoma, should open the door for additional expense-sharing on the restoration project. The project is expected to cost between $36 million and $48 million by completion, DuBay said.

To protect threatened and endangered salmon and steelhead trout, the 2008 biological opinion requires a host of changes in the way the water agency and the Army Corps operate the system through which 600,000 consumers in Sonoma and Marin counties receive their water.

One target of the opinion is the 13.9-mile stretch of Dry Creek north of its confluence of the Russian River. Operators of the water system are required to enhance or rehabilitate six miles of habitat by 2020.

The Army Corps until now has said it was not authorized to fund work outside of its own facilities or jurisdiction, a hurdle corrected by a section of the Water Resources Reform and Development Act signed Tuesday.

Another provision in the bill requiring studies of aquatic invasive species aids the Sonoma County Water Agency's work with the Army Corps on a mandatory watercraft inspection program for its reservoirs, Lakes Sonoma and Mendocino.