While you've been out enjoying Candlewood Lake during the late summer this year, you might have noticed that the water seems clearer than usual -- and you'd be right! This August, the water was the clearest it has ever been since the CLA began taking official measurements in 1985. While Candlewood might have been clearer earlier in its history, unfortunately we do not have the measurements to confirm that. Obviously the high clarity is good news, but it leaves us with some questions; namely, how did this happen and how can we keep the water this beautiful?
Before we get to that though, how do we measure water clarity in the first place? The answer is a specialized tool called a Secchi Disk. In practice, a secchi disk is pretty simple. It is a weighted disk with black and white triangles attached to a long rope. To measure the water clarity, you slowly lower the disk into the water until the very moment you can no longer see it. Then, you take note of what depth that is, and compare it to other measurements. The deeper the disk goes before disappearing, the clearer the water is! To help illustrate that is a picture of the disk right under the surface of the water, and next to that is a picture of the disk at a depth of roughly 4 meters (or 13.1 ft). We've circled the disk so it's a little easier to see in the accompanying photos.
We take a lot of measurements of water clarity, because it can indicate a lot of different important things about the lake, and the highest measurement we took this year was 5.41m (17.5 feet) in New Milford in August. The highest we've ever gotten anywhere on Candlewood since 1985 was 5.09m in Danbury Bay in 2006. To put these measurements into context, there have only been 5 years since 1985 where the average clarity across the entire lake for the year was above 3 meters. Even in May of this year at the same location, the clarity was 2.88 meters. So what is going on to make the water so clear?
Lakes are very complicated systems, so it can be hard to point to a certain thing and say "this is definitely what is causing the increase in clarity." But what we can do is make some educated guesses using the data, and what we know about lakes, to try to decipher the things that are contributing to what we're seeing in the water. Often times, in the late summer, clarity is lower because green and blue-green algae (AKA: Cyanobacteria) can grow and reproduce prolifically as the summer continues. This year, we are not seeing nearly as many of these organisms at the surface as we have in past years. Since these organisms are green, more of them means greener water -- which makes it a lot less clear.
There are a few possible explanations for why there are so few nutrients in the surface of Candlewood Lake this year, but the answer is probably a combination of a few things. Phosphorus and nitrogen usually end up in the surface water when rain grabs them as it hits the ground, and brings them into the lake. Rain grabs all the fertilizer we put on our lawns and gardens and moves it to lakes and storm drains -- which usually also drain out into our lakes! Instead of feeding the flowers and grass in our lawns, the fertilizer just ends up feeding the algae in our lakes, making our water green and unpleasant. This year, we've been lucky that hasn't happened, and that's likely due to a lack of rain, as well as all of you in the Candlewood Lake community doing your part and cutting down on fertilizer use at home!
While we know that the clarity is going to go back down eventually, we should celebrate the clear water we have this year and enjoy it. It's also all of our responsibility to try to conserve Candlewood and do the things, like saying "No!" to added fertilizer in our yards, that can help keep our lake beautiful for years to come.