Secchi disk

A secchi disk is like a giant frisbee that scientists put in water to see how clear and clean it is. When they lower the disk into the water, they can measure how far down they can see it. The deeper they can see the disk, the clearer and cleaner the water is!

When the water is cloudy or dirty, they won't be able to see the disk very far down. This could mean there's a lot of algae or other things in the water that aren't good for the animals that live in it.

So, scientists use the secchi disk to help them find out how healthy the water is and if it's safe for animals to live in. By tracking how clear the water is over time, they can also monitor changes in the environment and see if there are any problems they need to fix to keep the water clean and healthy.