The lack of rain and resulting low flow of the Russian River pose a threat to endangered coho salmon, which are having difficulty reaching their spawning grounds and could be caught and killed by fishermen.
Biologists are concerned about any harm done to coho, a fish which is being coaxed back from the brink of extinction but still numbers only in the hundreds.
A major difficulty brought by reduced rain is the fish are still in the Russian River's main stem rather than in the tributaries where they are usually spawning by now.
As a result, the Sonoma County Water Agency is distributing 20,000 cards with pictures and identifying characteristics at places where fishing licenses are purchased, in addition to the 20,000 printed two years ago.
"We kept hearing from people that there were coho in the river and we were hearing that the anglers would not be able to tell the difference and they would keep the coho," said Ann DuBay, water agency spokeswoman.
Bill Laurie of Santa Rosa, president of the Russian River Fly Fishers, said most fishermen know the difference, that coho have black mouths and steelhead have a white mouth. But he also acknowledged that the concerns of biologists and regulators are warranted.
"There are poachers and people who don't know how to tell one fish from another and there are people who don't care," Laurie said.
Two years ago, a picture of an angler holding a coho was displayed on the Internet page as part of the annual Russian River steelhead fishing contest.
Coho are in the Russian River now, but the low flow has cut them off from many of their tributaries, such as Grape, Green Valley and Mill <NO1><NO>creeks, where they go to <NO1><NO>spawn.
Instead, the coho are holding in river pools alongside steelhead that are legal to fish for and are now in the river in abundance.