A US$420M flood control dam has been built to safeguard three million people in the US. The 167m high Seven Oaks dam, on the Santa Ana river, has been erected upstream of the inland region east of Los Angeles.

The dam, opposed by environmentalists, is a key component of a US$1.5B effort to lessen the effects of catastrophic floods along the 75-mile course of the Santa Ana river. Critics worry that the dam, which is designed to hold back water only during periods of heavy runoff, could evolve into a semi-permanent reservoir, jeopardising its flood control objectives and destroying wildlife habitat.