Good question.
I've wanted to be able to test it in a few spots outta curiosity but never have.
I'd suppose close to the 1st, 2and and 3rd magnitude springs it's inevitable for there to be brackish waters to some degree but outside of the direct areas around them, not so much, it dilutes quickly.
The 'flats' areas and all up in around the barrier islands are very effected by the daily tides.
None of those areas seem to support freshwater fishes like the Everglades do.
The gators are even rare visitors.
A lot of springs people think are fresh water are actually salt water.
Just yesterday when the current storm front we're having was moving in we had a lot of associated wind, it coincided with a incoming high tide.
The tide pool behind my house looked like it had a fountain in the middle of it. There are natural crevices and possibly a small vent in the bottom of the pool. The tide was coming in quickly being pushed by the winds.
This forced the incoming saltwater to come ripping out of those crevices making it appear like a first magnitude spring.
I suppose it does qualify as being a spring of sorts, just not a freshwater one.
If you're looking at the map, I'm in the Ozello Keys in between Homosassa River and Crystal River.
