Fishing installations consisting of branches of trees, bushes or other soft vegetation stuck into the muddy bottoms of lagoons, lakes or rivers, are common throughout the world. Collectively, these may be termed "brush parks" and are found in many parts of west Africa, Madagascar, Sri Lanka, Bangladesh, Cambodia and China, as well as in Ecuador and Mexico. Two main types are common: (a) small, circular piles of branches sometimes surrounded by fences of more durable wood, and (b) larger, rectangular installations. Brush parks have usually been considered simply as devices for the attraction and concentration of fish, shrimps and crabs from the surrounding waters. However, one study in Benin has shown that the situation is in reality more complicated.