The U.S. Bureau of Reclamation has cut water releases from 1,100 cubic feet per second down to 500 feet.
"That has exposed some of the fall run salmon nests or 'redds' as they're called, r-e-d-d."
Tom Ghoring is with the Sacramento Water Forum.
On Capital Public Radio's Insight with Beth Ruyak, Ghoring said early surveys show that reductions, prompted by the dry winter, have left 15 percent of salmon nests or "redds" out of water.
"We know that exposing them is harmful to them. An exposed redd doesn't necessarily kill the eggs buried in the redd, but some of the nearby redds that are still underwater may be harmed so much that they could die."
~Tom Ghoring, Sacramento Water Forum
Reclamation officials say reducing water flows into the American River will help conserve the water supply stored behind Folsom Dam.
Insight will have more about how the lack of rain is impacting the region, coming up at 9 a.m.
January brought above-average rainfall and snow to much of California, partly due to El Niño. But forecasters say the ocean warming condition is "taking a break" for the next week or longer.
The U.S. Drought Monitor says, other than a slight reduction in exceptional drought in the northern Sierra, it needs more time to assess impacts of the recent moisture on California's long-term drought.
California regulators have made modest adjustments to water conservation requirements for cities.
The second measurement this winter of snowpack in the Sierra Nevada was 130 percent of average. State water officials say the snowpack will help reservoir recovery.
California's water conservation rate dropped to 18 percent in December. But water regulators say the state continues to meet its long term goals.