You don’t have to rent a charter fishing boat, but you can board a modest craft big enough for you and dad to explore the open lake for fishing or paddling. The exercise and sunshine will do you both good, and you’ll have plenty of scenery to look at (and some healthy competition if you’re both anglers).
If going out in a boat isn’t in the cards, you can opt to sit on the dock and cast a line while enjoying some peace and conversation. You can rent a children’s fishing pole and help them learn the ropes as a bonding experience. This can be an entire family outing.