On a trip to the boundary waters the leeches had just "spawned" (I guess they do this?) and with every paddle stroke in the shallows you would stir up a bunch of baby (wrong terminology) leeches. I was fascinated by this, my wife not so much. We also carried a bait bucket full of 12 dozen leeches for the 10 days we were camping/canoeing, best and hardiest bait up there by far, caught SMB/WE/NP like crazy.