In late 1975, construction began on the first "mini" theme park opened at the Walt Disney World Resort. River Country, a Disney version of an old-fashioned swimming hole, rests on the edge of Bay Lake in Disney’s Fort Wilderness Resort and Campground. It features flume and raft rides, a nature trail, and a large beach. This park gets its water supply from an intake/filter pipe in Bay Lake. Water is sent along the lake bottom into a pump system located inside River Country’s artificial mountain. From there it is forced down the flume troughs at about 8,500 gallons per minute, providing water for the flumes, and continually replenishing River Country’s water supply. A large rubber "bladder" separates the park’s water from regular lake water, with the help of a sensor system that keeps it inflated exactly six inches above the lake. Excess water from River Country spills over the bladder, replenishing Bay Lake. River Country opened in June 1976.