I have a problem with a nest of yellow jackets.The nest is located 1 inch above the waterline in my koi pond.Due to the location I'm not able to use poisen since this would kill my koi.I have flooded the pond and at night have used a powerwash sprayer several times but the bees are back.I also poured a can of salt in the opening follow by powerspray with water. I have a person coming monthly for maintanance and I'm afraid she'll be stong.
Any idea what I could do to eliminate the problem?