Complex sentence: For flood control purposes, some space in Oroville Reservoir has to be kept dry to capture floodwaters, a practice that has caused controversy at other dams of California over the amounts of water wasted.
Split into simpler sentences: For flood control purposes, some space in Oroville Reservoir has to be kept dry to capture floodwaters. This practice has caused controversy at other dams of California over the amounts of water wasted.