The annual fall Putah Creek salmon run typically starts in mid-November and can last into the first week of January.
What should be a banner year for the return of spawning Chinook salmon is instead facing a disastrous start.
Over the past decade, fall-run Chinook salmon started returning to spawn in Putah Creek in encouraging numbers. The return can be attributed to a collective effort of government agencies, volunteers and farmers.
Rich Marovich, Streamkeeper of lower Putah Creek for the Solano County Water Agency, has worked for decades to restore and increase the number of Chinook salmon returning to spawn in Putah Creek. The agency, he said, put up $175,000. for salmon study this year but noted one problem: “Now we need the salmon to study.”
Marovich said he thought they were well-prepared this year, but thus far only five large fish have been counted upstream.
“It’s shaping up to be perhaps the worst run ever if we can’t find out what’s going wrong and doing something about it,” Marovich said.
“Eighty-one Chinook have died on our doorstep,” Marovich said. The reason is low dissolved oxygen in the water and salmon need a high level of oxygen to survive, he said. To his knowledge, the low oxygen situation is “unprecedented.”
“Nothing like this has happened in the 20 years that I’ve been streamkeeper, so there’s something new going on. We really don’t understand it,” said Marovich.
Several hundred Chinook typically complete the run each year. A peak run occurred in 2017 with about 1,700 fish and their offspring were expected to return in three to four years, he said. Very few fish return after five years at sea due to the pressures of ocean fishing, so the 2017 peak run is not seeing the return numbers anticipated for 2021.
While low dissolved oxygen is a natural occurrence, it is not normal to persist for weeks. Levels do fluctuate and drop at night during respiration as oxygen is drawn out of the water and then increases during the day as aquatic vegetation releases oxygen into the water during photosynthesis. Yet the low dissolved oxygen level has dropped precipitously over the past three weeks and hasn’t shown signs of recovery.
Along the east levee of the Yolo Bypass is a toe drain that connects the mouth of Putah Creek to Prospect Slough, the Sacramento River and the Delta. Marovich said the water at the toe drain looks black as though it is loaded with organic matter and is so bad that it is killing carp.
Marovich drove around the 14,000 acres of the wildlife refuge and saw dead carp everywhere.
“Carp do not usually die from bad water. When you’re killing the carp then something is drastically wrong,” Marovich said.
As far as pollutants being placed in the water causing the low dissolved oxygen condition, Marovich said, “I don’t think you have to look for exotic explanations. Low dissolved oxygen is sufficient to kill fish and Instances of toxic substances are exceedingly rare these days.”
Although the condition has been reported to various agencies, Marovich is concerned that the call is not being met with urgency and expediency.
The water agency sent out a hydrologist to survey the dissolved oxygen in the toe drain and plans are in place to conduct a boat survey up from the delta to see how far the bad water extends back into the toe drain.
Marovich said the Delta Watermaster should be overseeing and preserving the Delta’s water quality. He wrote a letter regarding the water quality on Nov. 24. At this time, he said, “water quality is not being protected” and speculated that the low dissolved oxygen levels are created by low flow zones in the toe drain as water is diverted by agriculture, flooding for duck clubs and waterfowl habitats.
With salmon on decline and threatened, “The chance to establish native origin fish returning to establish a unique population in Putah Creek is important to the recovery of salmon as a whole,” Marovich said. “We could have potentially 3,000 spawners in Putah Creek each year,” he added.
Marovich said this situation is something they’ve not seen before and may take a while to figure out.
“We’re seeking answers and we don’t have them yet,” Marovich said.