Funny you made this thread, I was there yesterday early afternoon as well and I couldn't count the number of fish I saw dead on top of the water by the shore. I only saw Sunfish, had no clue there were Pike, Bass and Carp as well, at least this confirms those species really were present in there lol.
I thought, maybe some tool caught a couple and kept them until last minute and decided then to throw them back in, meanwhile it was too late, they were already dead.
However, I then saw TINY TINY sunfish too, which I had a hard time seeing anyone being able to catch even if they tried.
Some dude came by and told me the Conservation guys were there earlier trying to figure out what happened.
Definitely think someone put something in the water to cause them all to die, not sure what would cause this, but wow, they're all dead :S
Definitely please keep us updated if you find out anything else.
Before I post this, quick thought that comes to mind, maybe one of the MANY area residents and/or High Park regulars who were so unhappy with the anglers around there who leave such a mess and create hazards for wildlife, thought he/she would put an end to it. So many have been trying to ban fishing there for so long, I think at one point it was even temporarily banned? I dunno, only thing that comes to mind. No way did they just randomly all die.