Talk:Hazards/@comment-3064498-20110826114324

August 2011 - other hazards This is the story behind the fish kill in the West Arm. On Friday August 5th, we (MNR) got a couple of phone reports from tourist operators in the West Arm area. They reported a couple hundred dead fish – the species varied. We were unable to respond until Tuesday August 9th – at which time Paul Kennedy and I drove down there and put a boat into the West Arm at the hwy. We proceeded west and a bit south to an area just east of what people call “the cut”. Here we found an abundance of very fat fish eating birds – gulls, cormorants, ospreys and an eagle. On the downwind shore of the reach, spread over a couple hundred metres, we saw the remains of about 100 fish. Those that were still identifiable were all lake herring – also known as ciscoe – which are in the same family as whitefish. None of the fish we could examine had gill net marks on them. There were no signs of a spill. No easy way for a spill to happen at this location since there was no road or railway in the area. We did an oxygen/temperature profile at a couple of spots in the area. Basically, there was insufficient oxygen for fish life below about 5 metres in depth. And water temperature at that depth was over 24C. We went to one of the tourist operators establishments that had reported the die-off. There we picked up 4 frozen fish that they had collected from the kill-site on August 5th. They were all herring, and appeared quite healthy - if you overlook the fact that they were dead. No sign of wasting away or unusual parasite loads. The most likely and obvious explanation for this die-off is something commonly called ‘summer-kill”. Decomposing organic matter on the bottom of the lake uses up oxygen to rot. This causes a band of low or no oxygen water to form at the bottom after the lake stratifies in late spring. As the summer wears on, this band gets thicker, pushing fish towards the surface. At the same time, the band of water that is too warm for herring to tolerate forms at the surface and gets thicker as the summer wears on, pushing the cool-water fish down. When the band of water that is too warm meets the band of water at the bottom with too little oxygen, the herring become very stressed and succumb. This is no ones fault really and not much you can do about it. It tends to happen more in shallower water bodies with higher nutrient loads – a good reason for trying to keep phosphorus loading from man-made sources low (septic tanks, fertilizers, soil erosion) to avoid excessive plant/algae growth and subsequent decomposition. I hope this answers you questions. If not, give me a call 705-475-5512. Thanks, Stephen Stephen Belfry Fish and Wildlife Technical Specialist North Bay District