A.The horse flies in your area are likely utilizing the pond as their breeding grounds. They love warm and damp areas which are favorable conditions for the immature stages of horse flies. For control of the horse flies we would recommend using a combination of an IGR (Insect Growth Regulator) such as the Nygard IGR and a residual insecticide such as the Onslaught. Although treating the direct source of the infestation would be ideal for most pest control treatments, in your case it may not be the most ideal because the source is most likely near the beds of the pond. Most flies lay their eggs in the ground near the edge of the pond so that their larvae could feed on the insects near the pond. They also pupate inside the moist soil. Therefore treating the areas around the pond may contaminate the pond water causing all life inside the pond to die. Since you cannot treat the direct areas around/near the pond, you will have to be very careful and treat near but not close to the pond area and also consider not applying the pesticide during windy days because the pesticide can be carried by the wind during application and contaminate the pond. There is not guarantee of safety for the small reptiles in the area that feed on the insects exposed to the insecticide. With the decrease of the insect population in the area, it is also likely the number of predators in the area will also decrease. There is also a chemical free option by using fly parasites.