An extreme heat wave in the Southwest could pose a risk to Lake Powell’s water levels, which have been steadily increasing all summer.

After an extended drought period, Lake Powell, which is in Utah and Arizona, reached drastically low levels last summer, but levels began rising in earnest in April after California experienced a wet winter. The above-average snowfall in the mountains led to an increased snowpack melt that has continued to supplement Lake Powell, as well as Lake Mead in Arizona and Nevada, this summer.