PHOENIX (AP) — The Hopi Tribe and coal mining groups are suing an Arizona aqueduct system's operator to try to keep a coal-fired power plant alive beyond 2019. The lawsuit filed Tuesday in federal court contends the Central Arizona Water Conservation District legally is obligated to buy power from Navajo Generating Station near Page. The district's Central Arizona Project canals deliver water to Arizona cities and farmers. The plant's owners plan to close it and use cheaper energy from natural gas as various groups search for a new owner. District spokeswoman DeEtte Person said officials are reviewing the lawsuit and considered its impact. Person has said previously said the CAP is not required to take power from the plant and has other revenue sources to pay canal system's construction debt.