On May 10, 2025, Mason Valley resident Arron Hansen posted on social media that, “Today I went over to the Walker River irrigation easement with my wife to check on the river. We saw that several fish appeared to be ill and dying, floating to the top of the water. Started poking around a little bit, and it was kind of overwhelming the numbers that I was seeing. There were several species, including carp, sunfish, catfish and sucker fish. I documented it and took pictures and videos. A lot of the fish appeared to have red blemishes…We could probably count 20 or so fish floating around. Later in the afternoon, we decided to go check out other parts of the Walker River downstream and at Miller (Lane) Bridge. We were seeing more larger fish dead on the shorelines. I researched as much as I could to try to find out what was going on with the fish…I reported it to fish and game on their website.”
On May 11, 2025, Arron Hansen wrote: “These were all taken a few minutes ago from Miller (Lane) Bridge, Yerington (Mason Valley). These are all dead catfish, dead carp and dead sunfish.”
In response to Arron Hansen’s concerns, the Pizen Switch Times sent emails with Arron’s photos & information to Nevada Department of Wildlife NDOW and Nevada Department of Conservation & Natural Resources on May 12, 2025, including Lyon County Emergency Manager Taylor Allison in the communications.
On May 12th, Taylor Allison replied that she would follow up with WRID(Walker River Irrigation District), NDOW and NDEP (Nevada Department of Environmental Protection.
On May 28, 2025, NDOW’s Public Information Officer Ashley Zeme sent the following findings regarding the ongoing fish die-off in Mason Valley’s stretch of the Walker River:
“Hi Leah,
“Thanks so much for reaching back out and for sharing the new photos. I really appreciate your continued attention to this situation.
“While we had been coordinating closely with Lyon County, we were waiting for our investigation to conclude to confirm details before releasing information. I now have those findings, which I’ve summarized below. Fish die-offs caused by fluctuating water levels, such as in this instance, typically resolve on their own, and the original issue was believed to have been resolved. However, I shared this new photo with our Fisheries Division, and they’ve confirmed it’s part of the same die-off, which is being caused by continued fluctuations in water levels. We expect this issue to eventually resolve as conditions stabilize.
“Here’s what our original investigation found:
Our fisheries biologist visited the site on May 13, 2025, and determined the fish kill was likely caused by a sudden dewatering event, which impacted a 1.7-mile stretch of river both upstream and downstream of a drain located between the Mason Valley weir and Miller Lane. River flows dropped sharply from 90 cubic feet per second to 30 cfs just as temperatures started to rise, which is pretty normal during peak irrigation season. This sudden drop led to high water temperatures and low oxygen levels that can be lethal to coldwater species like trout. It also caused different species of fish to become stranded and unable to get back into the deeper water channel.
“Events like this tend to occur when flows drop rapidly, because fish don’t have a chance to move back into the main channel before conditions become critical.
“As mentioned above, we do expect this issue to resolve on its own as conditions stabilize.
“Please let me know if you have any other questions. I apologize for the delay in responding!”
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