New Waddell Dam, Embankment dam in Maricopa County, Arizona, United States

New Waddell Dam is an embankment dam on the Agua Fria River, north of the Phoenix metro area in Arizona, forming Lake Pleasant. The dam is part of the state water supply network and ranks among the largest earthen dams in the American Southwest.

The original dam, first called Frogs Tank Dam, was designed by engineer Carl Pleasant as a multiple-arch buttress dam and completed in October 1927 after decades of funding struggles; its inauguration was delayed to February 1928 after cracks were found. The New Waddell Dam was built from 1985 to 1994 as part of the Central Arizona Project, replacing the Orme Dam under Plan 6. In 1992 two arches of the old dam were breached so its reservoir could fill behind the new structure.

The reservoir's name, Lake Pleasant, comes from the former settlement of Pleasant, which lay in the valley before the water rose. The lake now covers the site of the old town and the original dam. The Central Arizona Project aqueduct delivers Colorado River water into it, and the lake also stores Agua Fria flows for the Maricopa Water District.

The dam itself is not open to visitors, but the nearby Lake Pleasant Regional Park provides boat ramps, campgrounds, and trails around the water. An early morning visit is especially helpful in summer, when desert temperatures can climb sharply during the day.

The original 1927 dam was not demolished but simply submerged when the new reservoir filled up, and its outline can sometimes be seen from the surface when water levels drop. Divers have explored the old structure underwater, making the lake an unusual spot for that reason.