Yes, there are many lakes, rivers and waterfalls in and around Panama.
The most famous lake of all is Lake Gatun, an artificial lake that played and still plays a crucial role in the Panama Canal. Thanks to a genius plan to dam the Chagres River and create Lake Gatun, the Americans were able to control the untamable river and complete the Panama Canal. Today, Lake Gatun serves as a passageway for the large vessels crossing the isthmus.
As for the waterfalls, the most beautiful ones can also be found in and around Lake Gatun.
Check out the following video to see what I mean.