You are less likely to take a dip in your pond, if you're attacked by leeches every time you enter. You won't so much as put your hand in the pond, if leeches come along and suck your blood. If you remove them incorrectly from your skin, they can leave behind mouthparts, which can cause infection. There is no proven way to kill all leeches in a water system without destroying the ecosystem and other life within the water. But you can severely reduce the population of leeches in your pond.
Poke several 1/8 to 1/4 inch holes in a coffee can lid with a knife or nail.
Place 1/4 cup of raw meat such as chicken, beef or liver in the bottom of a 0.454kg. coffee can.
Cover the coffee can with the plastic lid.
Submerge the can into your pond.
Place a rock on top of the pond to keep the can from falling over.
Check the can two times a week and remove it when you find leeches trapped inside. Kill the leeches by setting them on fire inside the can. Make sure to do this outside in an open area.
Remove rocks, sticks and other debris from the pond. Leeches prefer to hide under these types of objects; removing them will help reduce the leech population.
Apply a bacteria to the pond to clear the muck at the bottom. The muck, or mud, at the bottom of the pond is where leeches breed. Pellets that clear muck, such as Pond-Clear Natural Bacteria or Pond Logic MuckAway, utilise natural bacteria to eat away at the muck. This will also help reduce the harmful bacteria. You can obtain a muck clearer at a garden supply store or online. Throw the recommended amount of pellets for your size pond into the water.