If you can tie a few simple knots, you can make a fishing net. Nearly anything can be used to make a fishing net, but some materials are more effective than others. Some are even too effective. The key is to capture only the size and type of fish you want while catching as few of the smaller and less desirable fish as possible.
Most fishing nets are knotted together from nylon rope or other synthetic fibre lines, ranging from 2mm thickness for the net itself to 6mm thickness for the top and bottom drag lines. Some commercial nets have wooden or plastic booms at each end along the top of the net to encircle fish and drive them into the centre of the net.
A net sized for one or two person use in a creek, pond or stream would be about an arm's length wide to the left and right of the person holding it, and the net would be waist or chest high when in use.
Screw eye hooks into a wall or into two wooden posts at chest height just under 20 feet apart. Tie one end of one of the 20-foot long 6mm thick cords to the left eye bolt using a fisherman's bend knot. Thread six to eight 4-inch diameter foam fishing floats onto the top line. Tie half knots before and after each float to prevent them from drifting along the line. Tie the other end of the line to the second eye hook using a fisherman's bend knot. Space floats evenly along cord.
Cut 60 lines 8 feet long from the 2mm twine. Fold each line in half. Attach each line to the 6mm top line using a lark's head knot. Space lines 4 inches apart. Beginning 4 inches toward the floor, at the far left side of the top line, take the right cord of the first pair of knotted lines and the left cord of the second, and tie them together using a square knot. Continue from left to right until you reach the left cord of the second to last line and the right cord of the last line. Tie them together in a square knot. The far left and far right outer cords will be the right and left outside lines of the net.
Drop down 4 inches along each vertical line and repeat Step 2 until you reach the floor, making rows of knots every 4 inches. Every other row of knots will attach to the far right and far left outer lines. Just before tying off the final row at the bottom, tie each line to the second 20-foot long 6mm cord using lark's head knots. Be sure each cord is knotted 4 inches from the one beside it.
Attach split shot sinkers along the bottom of the net, evenly spaced every 4 inches. Your net should hang down about 4 feet when in the water, with the floats bobbing on the water's surface. If they are submerged, remove a few of the split shot sinkers until the floats are on the water's surface.
Untie one end of the top line from the left eye hook. Make a large knot at the end of the rope to prevent any floats from slipping off the line.
Be sure to check with your local fish and game warden to be sure your net is legal to use at your intended fishing site.