Common carp (Cyprinus carpio) and channel catfish (Ictalurus punctatus) die from low dissolved oxygen and ammonia that are the result of an over-application of biosolids.
Observation by Eric Augustino:
On September 23, 2013, I observed a fish kill in the Central Welland River located in the town of Wellandport, ON. Species included common carp and channel catfish. There were many dead and dozens more appeared to be gasping for air at or near surface of the water.
Local Conservation Authority contacted the Ministry of Environment to investigate. Testing revealed very low dissolved oxygen and toxic concentrations of ammonia. The Ministry of Environment investigation revealed an over-application of biosolids upstream.
Observations From Members 
Biosolids