Scores of scientists and academics are urging Marin County officials to crack down on development near creeks in the San Geronimo Valley to protect endangered coho salmon.

In a letter circulated by the Salmon Protection and Watershed Network, a number of fisheries experts and others assert that without tougher regulations, “development in the San Geronimo Valley will likely lead to extirpation of coho salmon from the watershed, making the recovery of coho salmon in the Lagunitas Creek watershed increasingly problematical.”

The letter, contending a regulatory measure under review at the Civic Center is too weak, says any development within 100 feet of creeks should be “strongly discouraged,” including occasional “ephemeral tributaries” or headwater drainage areas.

Thomas Lai, assistant director of community development, declined comment when queried about the letter on Tuesday.

Lai’s planning staff developed the creekside ordinance approved by a 6-0 vote of the Planning Commission that county supervisors will consider June 18. The measure limits creekside development but allows exceptions involving site review and permit procedures. The measure would apply to streams in unincorporated areas.

But SPAWN says regulations approved by the commission are riddled with loopholes. It noted the April letter, updated this month, was signed by 136 people, including salmon experts such as Peter Moyle of the University of California at Davis, and others, such as Sylvia Earle, a former top scientist at the federal National Oceanic and Atmospheric Administration, and John McCosker of Mill Valley, a noted fisheries researcher and former head of the Steinhart Aquarium.

Specifically, the letter asks that if allowed, any development within 100 feet of creeks “should require mitigation if new structures or activities reduce the potential for rehabilitation of riparian habitat, even if it is currently disturbed by lawns, patios, etc.”

Moyle said that because the San Geronimo Valley hosts one of the most important runs of coho in the state, regulating the headwaters there can affect the coho run along the California coast. A press release issued by SPAWN also quoted Debbie Sivas, a Stanford Law School professor, as saying Marin officials have developed an ordinance so weak it allows development that will jeopardize “the most important watershed we have left” for coho.

And Todd Steiner, head of SPAWN, claimed that the county measure “will legitimize more than half a million square feet of new construction in the so-called 100-foot buffer … . Is this current draft a conservation ordinance or a ‘coho salmon death warrant?'”

Critics assail the county ordinance as a land grab that will hurt real estate values. They note it regulates backyard activities, applies to drainage swales that are wet only after rainstorms as well as streams with no spawning fish, and contend the local coho population is on the rebound.

Strong opposition has been lodged by creekside property owners, the San Geronimo Valley Stewards, Sleepy Hollow Homeowners Association and the Marin Association of Realtors, among others.

Contact Nels Johnson via email at ij.civiccenter@gmail.com. Follow him at twitter.com/nelsjohnsonnews