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Since You Asked: Dissolved oxygen led to deaths of Expo pond trout

My son and I were at the Expo ponds late Tuesday and noticed a bunch of dead fish in one of the ponds. What gives?

— S.A., email submission

What you discovered, S.A., was a fish-stocking opportunity gone awry and the guys at the Oregon Department of Fish and Wildlife feel sick about it.

Cole Rivers Fish Hatchery had an extra 240 trophy trout ranging from 1-to-3 pounds, so they wanted to create a little excitement among urban anglers unable to drive to mountain lakes to catch their trout.

So on Oct. 21, those trout were stocked in Mace Pond at the Jackson County Expo area off Peninger Road.

On Wednesday, someone called the ODFW's Central Point office — it might even have been you, S.A. — reporting a raft of dead fish in the pond, says Dan VanDyke, the ODFW's Rogue District fish biologist.

VanDyke went down to the pond and helped remove 60 dead rainbow trout, but he also spied some largemouth bass and other warmwater fish alive in the pond.

Seeking a reason for the die-off, he tested the water and discovered low enough levels of dissolved oxygen to be lethal to trout, VanDyke says. The levels were much lower than at the other Expo pond normally stocked with trout.

"We saw no other signs of any other potential problem at the pond," VanDyke says.

The remaining fish seem to have survived — at least so far.

VanDyke says he hopes anglers will hit the pond to catch and keep as many of these trout as possible, provided they obey fishing rules and don't eclipse the five-trout daily limit.

That pond hasn't been stocked with trout in at least six years, and the chances of it getting more trout look slim without the pond passing a dissolved oxygen test first.

"Obviously we'll take a lot closer look before we ever stock there again, because we know there's a problem," VanDyke says.

Send questions to "Since You Asked," Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to youasked@mailtribune.com. We're sorry, but the volume of questions received prevents us from answering all of them.