The urban legend is that if you toss some pennies into a birdbath, the copper will help prevent the growth of algae. But any gardener who has tried this trick recently may be in for a surprise. Pennies minted after 1982 are not pure copper. In fact, they are made mostly from zinc, with just a tiny bit of copper. If you want to prevent algae growth in your birdbath or vases, try this instead: Pick up some copper wire or copper plumbing pieces from the home improvement store. The concentration of actual copper is higher, and it will do the trick of keeping the water clear.