Hydraulic mining was the largest and most destructive form of mining. Water, brought through flumes and ditches from high up in the mountains, was redirected into an ever-narrowing channel and out through a giant iron nozzle called a monitor. This high-pressure stream of water was used to wash entire hillsides through enormous sluices to recover placer gold. By the early 1880s, an estimated 11 million ounces of gold had been recovered by hydraulic mining in California. However, hydraulic mining had a devastating effect on the environment, causing pollution in rivers and streams. Because of the environmental issues and lawsuits brought by farmers, it was essentially outlawed in California in 1884.