Funny, you mentioned this. This past summer we went canoeing in the BWCA area. Bought two cups of leeches. We only caught a couple of fish. End up tossing it away because nobody wanted to carry it because we had more top priority things to carry.
Summer is probably the hardest season to fish
Lots of bugs, insects, and food for fish to eat and grow fat
Lots of variety
Its hard to get them to bite your bait
Try early spring
When the bugs are not out yet
Walleye love them leeches and worm