The San Francisco Bay Regional Water Quality Control Board has sent Stanford University a letter saying the agency supports "alternatives that focus on dam removal" as the university moves toward a decision on what to do with Searsville Dam and its reservoir.

The dam is located off Sand Hill Road west of Interstate 280, in the Jasper Ridge Biological Preserve on Stanford land.

The letter is dated March 30 and signed by Bruce Wolfe, executive officer of the water board, which is a state agency.

"We have been, and continue to be, supportive of alternatives that focus on dam removal," the letter says. The dam "remains a complete barrier to steelhead migration, greatly reducing the amount of habitat that is accessible, and placing this steelhead population at much greater risk of extinction," it says.

The dam was built between 1888 and 1892 by the Spring Valley Water Company, and was supposed to supply water to San Francisco, but the water was foul-tasting and was never used as drinking water.

Stanford acquired the dam and reservoir in 1919.

In 2013 Stanford announced it was studying the fate of the dam because the reservoir is more than 90 percent filled with silt and could be completely dried up in another 20 years.

Among the options being studied are removing the dam, restoring the reservoir through dredging, allowing the reservoir to completely fill in, partially excavating the reservoir, or diverting water to another area such as Felt Lake.

Stanford now uses water diverted by the dam, when water is available, for uses such as irrigation.

Stanford had said it would make a decision on the fate of Searsville by the end of 2014, but the university has not yet made an announcement.

In the meantime, environmental groups have sued the university, saying the dam and water diversions by Stanford are threatening endangered species, including steelhead trout and the red-legged frog.

Last year the American Rivers foundation named San Francisquito Creek the fifth most endangered river in the US because of Searsville Dam.

"Stanford University's 65-foot Searsville Dam blocks threatened steelhead from reaching 20 miles of habitat upstream, impairs water quality, and poses flooding risks for local communities," the organization said.

The organization Beyond Searsville Dam has been fighting for the dam's removal for years. Matt Stoeker, director of the group, and one of the producers of the documentary "Damnation," said the letter from the water board is "a powerful message supporting the removal of Searsville Dam, while also questioning the feasibility of other potential alternative futures for the dam."

Mr. Stoecker said that "the letter also stresses the importance of safely restoring the flow of beneficial sediment downstream for the health of San Francisquito Creek and to improve the resiliency of listed wildlife, San Francisco Bay wetlands and coastal communities facing the adverse impacts of climate change and sea level rise."

The letter was addressed to Jean McCown, director of community relations at Stanford and co-chair of the committee looking at alternatives for the dam. Ms. McCown did not immediately respond to a request for comment on the letter.