I've visited eight springs that are to the north of Orlando. The springs of Central Florida are among the great treasures of the USA and are swimmin' holes out of some exotic fantasy. The four closest to Orlando are Rock Spring at Kelly Park, Blue Spring State Park, Wekiva Spring, and Gemini.
It's cold water swimming and snorkeling - definitely bring snorkel gear. Everybody winds up going in, but it does take some serious getting used to. Once you're in, then you're ok.
Both Rock Spring and Blue Spring are runs - as soon as the water comes up, it creates a riverway to swim in. Rock Spring is very shallow and does widen to a landscaped area with some retaining walls. Blue Spring is bigger, deeper, wider. Both are very beautiful and a lot of fun. Wekiva is a beautiful sppring where retaining walls have been built around the spring (1930's?) to create a large pool. This is quite a shady spring, so the water will be cooler at the surface. Some nice trails around the spring.
Further north, there are another four springs, Deleon Springs State Park, Juniper, Alexander, and Salt. The last three in Ocala National Forest, quite a bit aways from Orlando. Juniper is the most beautiful and you might recognize it from magazine covers. Salt Spring is spectacular and large, Alexander the most natural, and Deleon has been made into a pool and is the least natural. However, at Deleon Spring is a fun old mill pancake restaurant where the flour is ground right at the mill. Griddles are built into the tables and you cook the pancakes yourself at the table. This is loads of fun. but I don't see any point in going swimming at Deleon, since it is like going swimming in a pool (albeit with no chemicals).
The following website is THE website for visiting the springs:
http://tfn.net/Springs/OtherCentralFloridaChapter.html