Cleaning
To make cleaning easier choose a bird bath that you can pick up easily, or choose one with a removable basin. There are some with a drain; be sure to get this type if the bird bath or basin is too heavy for you to lift.
Empty the old water from the bird bath by dumping or draining and rinse with a hose. Scrub the basin with a brush or a scrubber to remove algae and debris. Scrub with bleach to kill off the algae and to remove any stains. Rinse thoroughly and fill with fresh water.
The more often you clean out your bird bath the easier the job will be.