Take a bag to the beach. Bring a bag to pick up garbage that others leave behind. You may be surprised at what you find. Much of it will be empty cans and plastic food wrappers, but you may also find plastic fishing nets, buoys, lines, and even old rubber boots lost from fishing boats. Use biodegradable plastic bags.
Most plastic bags take a very long time to break down, or rot.
But some bags, like those used by Shaw's and Shop 'n Save Supermarkets, break down in three to five years. Ask for them when your family goes shopping. Teach one other person something about the ocean. It may be a friend, a parent or a grandparent. We all tend to take better care of what we understand and appreciate.