A meandered lake is one whose mean high-water line (at the time, according to the surveyor's judgment, based on existing vegetation, with emphasis on trees) was meandered (surveyed) by the original government surveyor. Only the bodies of water that were considered important or significant were shown on his survey.
So, as a practical legal matter, bodies of water that were not shown on the orgiginal Township Survey did not exist. So, if the US Govt. patented out land that contained an unmeandered lake the grantee owned everything within that legal description, including any lake. As did all subsequent buyers.
If your concern is the lake bottom of a meandered lake that gets exposed by drought, don't be worried that someone will come along and clain it. The State of Florida owns it. And from your lot line at what was once the mean highwter mark, and shown as the meander line, you can go across it any time you want get to the actual water.
The State has control of over dock building. Each case stands on it own.
If the lake is not a meandered lake, that another set of circumstances.
You may be correct about the State owning the lake bottom of any lake that is more than 30 acres in size. Sounds like a Realtor rule of thumb, or else a recent action taken since I quit selling real estate. Can you cite the legal source? Not that I don't believe you. I'd just like to read the actual source.