Adventures in Rainbow Country S01E22 - Lake on Blue Mountain

Those two intrepid fishermen, Billy and Pete, hike into the mountains to visit their secret fishing place - a jewel-like lake filled with fine pike. To their amazement, they find that the fish are dying and it appears that bush pilot Dennis Mogubgub has something to do with it. Horrified, the boys try to trap and remove the fish to another lake before it's too late to save them. That's when they learn a lesson in conservation.