I use an electric pump that is brushless to maintain our pond level. The pump will pump 5500 gph with a 2". Very little hydro and pumps up 25 feet. I have had minnows go through the pump but are not in very good shape when in the pond.

Like stated above if there is minnows or fish in the river that are a concern to you and your plans filter the water and start pumping.

Cheers Don.

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7/8th of an acre, Perch only pond, Ontario, Canada.