The massive fish kill in Louisiana

It appears to have been secondary to an anaerobic "dead zone," similar to the famous "jubilees" in Mobile Bay, Alabama:

The large volume of crab and fish that a jubilee can produce is hard to overstate.... author Archie Carr comments that "at a good jubilee you can quickly fill a washtub with shrimp. You can gig a hundred flounders and fill the back of your pickup truck a foot deep in crabs."