When we're out in our kayaks, we pick up bottles and bags floating in the lakes and bays.
It doesn't take much effort. And it's really worth it. Trash takes a long time to break down. Every summer there's a clean-up day here in the Gorge, and volunteers take away heaps of trash. There are kayak rental places in Toronto that give renters a price break if they come back with a bag of trash picked up during the boat rental.
A speck or two of plastic does no good but isn't much trouble to a large bird. But albatrosses have been found with their bellies full of plastic. It doesn't digest, and it can blog the animal's stomach, killing it.
Even a few bits of plastic cause problems to smaller animals, with BHP and other chemicals affecting the animal's health if it doesn't choke outright. It's enough to make me resolve that when my plastic kayak is finally at the end of its useful span years from now, the plastic will be recycled instead of put in a landfill.