The main purpose of this legislation is to manage the water levels of Flathead Lake in Montana. Specifically, it aims to maintain the lake at a certain level during the summer months to support local ecosystems, recreational activities, and possibly the local economy. The key provisions of the law require the Secretary of the Interior to regulate the water levels of Flathead Lake between June 15 and September 15 each year. The law mandates that the lake must not fall below a minimum level of 2892 feet above mean sea level (MSL) and must not exceed a maximum level of 2893 feet MSL.