To make a fish trap, realize it will take a long time. You should completely block the side against the current, do the sides, and leave a narrow opening, or doorway, at the down current side of the trap. The fish will enter the trap and they usually move up current once inside. Most will not be able to find the exit, so you'll have dinner! Use green limbs to construct the trap.
To catch the fish, you can make a net from a tee-shirt, sock or even weave one if needed. It may be possible, if there are more than one of you in the group, to stand close together and "drive" the fish into a corner, where you can collect them by hand. Keeping mind so fish have spines and other may have teeth, so you may want to make a fish spear, as illustrated below.
This shows how to make a very effective spear for catching fish. Use (1) green wood for the spear, (2) split it down the middle a little, and cut notches in thesplit end. It may be required to be reinforced where the split stops (by wrapping with wire or vines) to keep the split from growing larger. Use either a very brittle or limber piece of twig to keep the "Jaws" open as seen in figure 3. Carry a bunch of #3, twigs, in your pocket so you can catch more than one fish. It will take some getting used to using, because of the water refraction, the fish will not be located exactly where it appears to be to your eyes. You may have to aim slightly above or below the fish to spear it. It's a good tool, because in most cases it will hold the fish long enough for you to get it.
make fish trap