Diamond Lake, United States offers 1 beach perfect for sunbathing, surfing, swimming, and more. Diamond Lake, Oregon, United States, is known for its proximity to Crater Lake National Park and the Umpqua National Forest. The best time to travel to Diamond Lake, United States, is during the summer months of June to August, when the average air temperature is around 70°F (21°C) and the water temperature is approximately 65°F (18°C). Sandee provides detailed maps, photos, and reviews from fellow beachgoers to help you Choose Your Beach™ and plan your perfect beach vacation!