Brown Trout Fungus, Mr. Fungi

In this video is a wild brown trout fungus. Mr. Fungi in the video has this fungus covering much of his body. This clip is best viewed in 720p.

http://youtu.be/eiiTQV2_U60

As the brown trout spawn tapers off each year I see many browns get covered by fungus and ultimately die. Usually they are all larger fish (16+ inches). I've talked with local biologists about it and they tell me spawning takes a lot out of the fish and the old trout often die. I believe there is truth to that, but I've only seen numbers of brown trout suffering from the fungus in the last decade or so. Previous to that I don't recall seeing many. This leads me to believe there is something else killing our browns. Water quality? Parasites? Fertilizers and pesticides? I'm not sure what the problem is, but no one seems to want to solve the problem.

Are any of you fellow fly fishers biologists? If so, do you have any thoughts on this matter? I welcome your comments or suggestions.