Dealing with Duckweed

After the devastating effects of the unbelievably intense deluge of August 28, things at Blue Grotto are largely back to normal. Water clarity has returned and Virgil, who had gone five weeks without human companionship, is happy as a clam.

We say “largely back to normal” because there is a remaining issue, one that has not bothered us before. We now have an outbreak of duckweed. Fortunately, we have been able to manage it, so it is more of a minor annoyance than a real problem.

Still, if you have visited us in the three weeks since we re-opened, you no doubt noticed the patches of green stuff lurking at the very edges of the open water basin. You may have wondered what this is and whether it is something you need to worry about. (It isn’t.)

This article will tell you more about duckweed and what we are doing to manage it.

What duckweed is…and isn’t

Duckweed is not “pond scum.” Nor is it a form of algae. Duckweed has been characterized as “the world’s smallest flowering plant.” A plant with neither branches nor roots. Each duckweed is just a single leaf. A collection of duckweed has the consistency of finely chopped salad greens.

Duckweed reproduces asexually at a rate that would shame the most libidinous of bunny rabbits. Unchecked, it would cover the entire surface of the Grotto in no time. This would cause divers exiting the Grotto to be covered in duckweed, resembling the lead character from the movie Swamp Thing. That is not acceptable.

Managing the issue

We could eliminate the duckweed with herbicide. Doing so, however, might harm our resident fish and turtles. This is something we would never do.

The Blue Grotto staff has come up with a way to at least manage the quantity of duckweed and keep it from getting out of control. This involves two staff members getting the water and scooping up large quantities of duckweed with a large towel. This short video will show you how we do it.