A rectangular piece of netting made from nylon twine, gill nets can be anywhere from 900 to 1,800 feet long and are suspended from a line of wood or cork floats; lead sinkers attached to the bottom weigh the nets down and keep them taut. Regular applications of linseed oil and copper sulphate leave the nets clean and pliable. The copper sulphate solution, called “bluestone,” also tints the nets and makes them less visible in the water. Because the migrating fish avoid nets on sight, gillnetters working in clear waters generally set their nets at night. Rivers that are murky, like the Fraser, the nets are set by day as well.