Black Spot Disease

The lower Deschutes is an emotional subject for many with claims and counter claims often made by the many parties studying the issues affecting the river.  A current example of this is Black Spot Disease.  Technically an infection and not a disease, the black spots are caused by a parasite that exists across North America including many rivers in Oregon.

Multiple scientific articles state that the parasite generally does not harm fish although there have been cases reported in other states where heavily infected fish were blinded by cysts that form around the parasite. This level of infection has not been reported on the Deschutes.

Per ODFW, reports of Black Spot Disease are increasing across Oregon.  Black Spot Disease has been recently reported in the Metolius River.  It is possible that infestation rates may be increasing due to environmental changes although other causes are possible and there is no definitive answer at this point.

In an 8/12/17 blog post the Deschutes River Alliance posits that changes in the water temperature regime in the Lower Deschutes from the operation of PGE/CTWS’s Selective Water Withdrawal tower has increased the prevalence of Black Spot Disease.   This argument does not explain the increase of Black Spot Disease in other Oregon rivers, however, including those above the SWW.  It is possible that increases in Black Spot Disease could be another example of the impact of a warming planet.  See PGE’s take on Black Spot Disease in an 8/31/17 blog post.

I do agree with the DRA that additional studies should be done on this topic.  To my knowledge, none are being planned by ODFW, PGE/CTWS, or the DRA at this time.