The Bell Museum of Natural History in Minneapolis uses a slight variation called the Erickson Net which was designed by Jim Erickson who studied the banded darter in Minnesota. The hoop is rectangular with a frame made of rebar and a sock three to six feet deep. This much heavier net does work very well when held stationary in riffles, but peaks in performance when slung over the back and dragged through riffles. It really catches the fish and is exceptionally selective for darters. Any direction through a riffle works - upstream, downstream, or even across.
Tall people can hold it in one hand about mid-handle and brace the butt against a shoulder blade.
The net's only drawback is rapidly fatiguing the operator because of the great weight and resistance especially in swift currents. Regulations vary from state to state. Minnesota permits a hoop net up to four feet in diameter, but can't be used for a short period in the spring when the walleyes are running. Texas recently banned dip nets state-wide. Where this occurs, a potential option may be a special use or scientific collector's permit.