Complex sentence: The dam raised the water level 12 feet, causing the lakes to effectively merge into two lakes, north and south, as the water narrows considerably for about 0.4 miles near the community of Lake Leelanau.
Split into simpler sentences: The dam raised the water level 12 feet, causing the lakes to effectively merge into two lakes, north and south. The water narrows considerably for about a mile near the community of Lake Leelanau.