Why does our coastal water color change from time to time? Why does the same area look clear at certain times but opaque at others. Sometimes it’s an emerald green, sometimes it’s a murky brown, and sometimes it’s hazy blue. There are two primary factors contributing to these fluctuations: seasonal temperatures and short-term weather conditions.
When you’re out enjoying a day of boating in the summer, you’ll notice the prominent green hue to our coastal waters and reduced visibility. This has to do with the seasonal water temperature. In the summer, when the water is in the 80’s, and even 90’s, algae begins to bloom, fueled by natural processes but also boosted by fertilizer runoff from local lawn and garden maintenance. The algae thrive on phosphates and nitrates in fertilizer just like other plants, so along with our lawns, the water is greener as well. In the winter, however, the water temps drop into the 60’s and most of the algae die off. This clears the green out and returns it to the blue color you see from December to May.
As for the various shades of brown, well, that’s a more short term effect caused by local weather conditions. A sustained wind over 15 mph can churn up the shallow waters in our area and create a solution of suspended sediment that spreads throughout the system. Similarly, heavy rains will wash sediments from the land into the water and create murky conditions. It will often take about a day of calm weather to settle back down to the bottom.
So, the biggest contrast in water color and clarity you will see is between cool, calm weather periods with no precipitation and a hot, storm addled period with lots of runoff. Here in West-central Florida, that’s the stark visual difference between a day in April versus a day in August. If there’s one thing that’s certain in this world, it’s change- both short and long term. Even if it seems like something as trivial as water color, it can be a predictor of larger affects on our boating life from fishing conditions to safe navigation.
Do you know why Tampa Bay is brown? It’s been this was for a few months now. I figured it would settle down as the blog suggests, but it hasn’t. From Harbour Island to Beer Can Island and even farther. It looks like rusty water. Thanks!
Ms. Missana,
Thank you for that feedback! To understand an area like Tampa Bay, take a look at it on Google maps. While the coastal waters are bounded on only one side by land, Tampa Bay is surrounded on all sides. This means it is subjected to constant runoff from the surrounding properties. Not only will this contribute natural biological sediment content, but fertilizers and pollutants are coming into it from all sides as well. The bay should always appear less clear than the beach water, simply because it has less natural flow. It will begin to “blue” a bit this winter as rainy days become less frequent, the water temp drops, and some of the algae begins to fade.