A traditional Shoshoni weir (tribal museum).

We can think of the weir as two conical shapes: a big one on the outside, and a smaller one inside. Both shapes are made by placing lengths of willow in a circle. The outer length determines how long the weir will be. The inner length will create the inner circle.

The size of the inner circle is important: too big and the fish escape; too small and they won't enter.