Dead fish — as many as 100 — have turned up on the banks of Putah Creek in the UC Davis Arboretum. The situation has left many people wondering if there’s a link to the aerial insecticide spraying that was done last week to control for mosquitoes carrying West Nile virus.
“It’s more a function of weather,” explained Andrew Fulks, Putah Creek riparian reserve manager for UCD. Fulks received a report on Monday from the Sacramento-Yolo Mosquito & Vector Control District that detailed the insecticide’s concentration.
According to Fulks, the report showed that the two aerial “bursts” last Wednesday and Thursday over Davis and Woodland resulted in 0.0071 parts per million of Trumpet, an insecticide said to pose low risk to humans and the environment.
Fulks explained that a lethal concentration for fish would be 2.4 parts per million.
The timing of the fish deaths coincided with the spraying. But every year, fish suffocate in the poorly aerated water of Putah Creek in the Arboretum.
An algae bloom recently died and consumed much of the oxygen in the water, Fulks said.
“The color of the water has changed, it’s more brown now, typical of when algae is dying,” he explained.
As the Arboretum’s creek is very linear and shallow, and all the runoff from campus goes into the creek, it’s even harder to control the oxygen levels in the water. There also is a lot of organic matter in the water, which is very nutrient-rich, Fulks noted, and none of it is good for the fish.
The fish that are dying “seem to be carp, sunfish, suckers — warm-water fish,” Fulks said. No other wildlife have been affected.
“You wouldn’t see just one or two species dying because of the chemicals” from the aerial spraying, Fulks said.
Because the part of Putah Creek that runs through UC Davis’ Arboretum does not recirculate properly, a redesign is in the works. Andrew Fulks said that Arboretum staff are working with design consultants to introduce treated campus water into the creek, thereby constantly replenishing it with fresh water.
Reported Fulks, “The infrastructure is already in place, and we ran it as a temporary project for three years.” During that time, the recirculating water was very successful in reducing the big algae blooms, and they saw a drop in fish deaths.
There are three phases to the five-year plan. Although a bit of replumbing is needed, Fulks expects the new plan will have treated campus water going into the Arboretum in the next 18 months.
A call to the Stonegate Country Club verified that the dead-fish problem has not been seen in other lakes in Davis.
Griselda Jarquin of Stonegate said she hasn’t seen any dead fish or other creatures around the lake’s banks, and a check with the country club’s maintenance staff confirmed this. But unrelated to the spraying or the algae bloom at the Arboretum, the maintenance worker did note a higher-than-usual number of dead fish on the banks of Stonegate Lake a couple of weeks ago.
Seeing many dead fish in Putah Creek, a normally picturesque waterway, has been disturbing for local residents.
John Reeves walks along creek paths three times per week. He’s done this for the past 10 to 15 years, but it wasn’t until Friday that he noticed big, carp-looking fish near the surface of the water. Carp typically are bottom-feeders.
“I didn’t even know there were fish this size” in the Arboretum, Reeves said.
Initially, he thought it was turtles sticking their noses up, then he realized it was big fish breaking the surface, seemingly for air.
Monday’s walk was a different sight, with at least 100 dead fish along the creek’s banks, Reeves said. He detailed seeing about 30 fish dead on the shore, where Arboretum workers had scooped them into a pile.
Along another mile or so, he estimated seeing another 70 or so dead fish floating in the creek.
When asked if there appears to be more algae than he’s used to seeing, Reeves said, “The creek doesn’t look any different right now” than it has all season. He admitted that “it is sort of a murky creek no matter what,” and he is used to seeing it between 6 and 10 inches higher in wetter years.
Reeves also noted that the ducks, herons and turtles all looked fine on Monday.
In fact, Fulks said Arboretum staffers have said there have been sightings of otters and turtles munching on the bounty of fish.
Fulks also wanted to point out that “most of what we have in the waterway is either pets or game fish.” The non-native species of fish that show up in the Arboretum’s creek include carp, koi and common goldfish.
A couple of weeks ago, as Fulks was doing some volunteer cleanup along the creek, he pulled up an intact 10-gallon aquarium. Someone apparently dumped their whole tank into the water.
— Reach Tanya Perez at 530-747-8056 or firstname.lastname@example.org. Follow her on Twitter at @enterprisetanya