My Pond Is Killing Birds

I came home the other day and noticed a dead bird floating in my pond. I'm still not 100% sure how it dies, but I am assuming it drowned. I asked for help, and I was told a few things. I was told that the bird probably went in to get a drink, and the water soaked up in it’s feathers until it drowned. The pond, being a plastic tub, gave no where for it to crawl back out.