I took this from the U. of Ohio web page.
I left off option #4. Spraying of insecticides. ........ For obvious
reasons.

Adult Control
Option 1: Cultural Control - Hand Picking By noticing when the first
adults arrive on a property, you can pick off and destroy these scouts
that attract additional pests. The adults are less active in the
early-morning or late-evening. They can be destroyed by dropping into
a container of soapy water.

Option 2: Cultural Control - Plant Non Attractive Plants The adults do
not like to feed on ageratum, arborvitae, ash, baby's breath, garden
balsam, begonia, bleeding heart, boxwood, buttercups, caladium,
carnations, Chinese lantern plant, cockscomb, columbine, coralbells,
coralberry, coreopsis, cornflower, daisies, dogwood (flowering),
dusty-miller, euonymus, false cypresses, firs, forget-me-not,
forsythia, foxglove, hemlock, hollies, hydrangeas, junipers, kale
(ornamental), lilacs, lilies, magnolias, maple (red or silver only),
mulberry, nasturtium, oaks (red and white only), pines, poppies,
snapdragon, snowberry, speedwell, sweet pea, sweet-William, tuliptree,
violets and pansy, or yews (Taxus).

Option 3: Cultural Control - Trapping Several traps using a floral
lure and sex attractant are available. These traps are not recommended
for general use unless special conditions can be met. The traps have
been demonstrated to be effective in reducing damage and populations
only when landscapes are isolated from other Japanese beetle breeding
areas or when mass trapping (everyone in the neighborhood) is used. In
most urban areas, traps tend to attract more beetles into the area
than would normally be present. In this situation, adult feeding and
resultant grub populations are not reduced.

"Don Cunningham" wrote in message
news:3f0dc3a6$1_4@newsfeed...
We have them by the millions. They are swarming the pond. My fish
aren't big
enough yet to enjoy them as a snack, and they are causing a real
problem.
There are so many and they give off an oily substance that has
turned the
water reddish brown.

Anyone know how to deal with this?

don cunningham