Every few weeks, we’ll get an email in which someone asks, “What’s the water temperature this time of year?” Of course, if you’ve watched our orientation video or visited our website, you know that, with few exceptions, our water is a constant 72° F year-round.
It’s understandable why divers who have never been to north-central Florida might ask this. In most of the world, water temperature can vary widely throughout the year.
Take, for example, the typical Midwest rock quarry. In the summer, surface temperatures can approach and even exceed 70° F. Six months later, that same water can be frozen solid.
Below the deepest thermocline, however, the story is different. At Pearl Lake near South Beloit, Illinois, for example, temperatures at depth seldom exceed 40° F. This is because water temps below the thermocline reflect average groundwater temperature, not air temperature.
This helps explain water temperatures in north-central Florida’s freshwater springs. Because our water is constantly in motion, it never stratifies into layers. It remains the same from top to bottom.
The farther south you go, the warmer groundwater temperatures become. At our latitude, this just happens to be 72° F. This is an ideal temperature for divers.
The only time this changes is if the water stops flowing. This can happen during periods of extremely high water levels. In 1963, when Tom McQuarrie purchased what was to become Blue Grotto, North Florida had just experienced a series of powerful hurricanes.
Because of this, the water just wasn’t moving, and it would be a long time before it dropped to what we now consider normal. As the sun beat down on the same water, day after day, temperatures rose, and an algae bloom erupted. For a long time, it appeared visibility might never improve.
These days, a much tamer version of this phenomenon occurs only once or twice a decade. Otherwise, the water remains a constant 72° F and is clear from top to bottom.
So, as you can see, air temperature has little effect on water temperature at the Grotto. This is in contrast to almost anywhere else you might dive. It also begs the question, what is the ideal exposure protection to wear when diving here? We address this in a separate article — just follow the link below.