Horse flies and deer flies are biting insects that are drawn to water, movement and carbon dioxide. This makes people in pools an attractive target. The flies are especially active on warm, still days when you are most likely to want to use your pool. Getting rid of the flies involves the use of insecticides around the pool area, along with setting up a trap using a dark ball on a rope. The flies will be drawn to the dark colour and the movement of the ball as it swings.
Spray any shrubs or vegetation around the pool with a horse fly insecticide designated for use on plants. Follow package instructions for application.
Set up a battery-operated fan near the pool. For larger pools, set up one at each end. Horseflies are particularly active on still days, so the wind from the fans may help deter them.
Cut a piece of thin rope to a length of 12 inches. Use duct tape to tape a medium-sized black ball to the end of the rope. Tape the other end of the rope to the bottom of a stool. The stool should be at least 2 feet tall.
Press fly paper onto the bottom of the stool, around the spot where the rope is attached. Set the stool on top of a table that is at least 10 feet away from the pool. The flies will be drawn to the ball, and will get trapped in the fly paper when they fly upward upon realising the ball is not a food source.
If you have any marshes or swampy areas near your pool, consider having them professionally drained.