The Waikato River is the longest river in New Zealand, running 425 km from Lake Taupo to empty into the Tasman Sea. It has significant cultural importance to the Tainui iwi and is a source of their mana. The river provides hydroelectric power, generating 13% of New Zealand's electricity, and was an important transportation route. However, studies have shown that 75% of bacterial contamination in the river comes from dairy farm runoff, with many farms allowing livestock direct access to streams. While the city of Hamilton also impacts water quality, dairying has been identified as the primary contributor to unacceptable pollution levels in the Waikato River.