Question
Hi Brigitte:

I live in Alden, MI on the west side of the state near Traverse City. I have a
lined pond of about 15,000 gallons with a circulation pump that keeps the
water moving. I intended it to be something I would swim in as well as a
habitat for amphibians and have encouraged the growth of natural plants
around the pond. I put 12 feeder goldfish in there as well as snails, and
freshwater scooters that feed on decaying plant material. As they say, if you
build it, they will come!!!!! A number of water insects have moved into the
pond and the toads and frogs have spawned and it's full of tadpoles of
different sizes, species, and stages of growth. So far so good.

Today when I was removing spirogyra algae, I was grossed out to find I had
leeches in the pond. They were brought up tangled in the threads of algae.  
They creep me out and I don't want to swim in there with them. I know there
are different kinds and not all of them suck blood but I want them gone. Do I
try to trap them? I Googled how to catch them. I don't want to use chemicals
etc here because I don't want to harm anything else. How the hell did they get
in there anyway? Did they come in on a frog, or the pair of mallards that
visited this spring? The green heron that came and snagged a slow frog?
Could Rocky racoon have dropped one off? I read about using salt to kill them
but how would I ever figure out how much exactly to use, since I'm not sure
of the exact amount of water in there.

By the way, the pond was clear until the last few weeks when I've had a real
bloom of algae. I don't expect or care if the water isn't crystal clear, it'd be
nice but........... I just don't want the leeches in there!!!!!!!!!!!!!!!!!!!!!!

Thank you for any advice you can give me.

katie

PS: I suspect the algae is being fed by the leaves that got in last fall. I'll put a
leaf net over it this fall and see if cutting down on the amount of organic
material going in will cut down on the nutrients in there.


Answer
Hello Katie!
I am not a big fan of leeches myself, but some are quite harmless.
I am also not sure how to get them all out of there.
In smaller lined ponds, you can take fresh stew meat, tie a string around it and let it dangle in the pond for a few hours. Then you can just throw it and any attached leeches away. You repeat the procedure until the bait keeps coming up empty.
I suspect though, that you would have to use enough stew meat to feed an army in a pond that size.
You can use salt. It would take A LOT (have to use 100% pure salt: pond salt or solar salt) and you would have to take all the plants out.
High salt solutions will kill the plants (the fish can take quite a bit).
You would have to get it past .3 ppm.
It would take about 10 lbs per 1000 gallons to be effective.
Plants MUST be removed or they will die for sure. Fish can take it for a short period of time, but they must be observed for signs on stress.
It would be quite an undertaking for a pond that size.

Not sure how they got in there, but all the methods you mentioned are possibilities.