Mission Bay is an artificial, saltwater bay located south of the Pacific Beach community of San Diego, California, created from approximately 2,000 acres of historical wetland, marsh, and saltwater bay habitat. The bay is part of the recreational Mission Bay Park, the largest man-made aquatic park in the United States, consisting of 4,235 acres, approxi…Mission Bay is an artificial, saltwater bay located south of the Pacific Beach community of San Diego, California, created from approximately 2,000 acres of historical wetland, marsh, and saltwater bay habitat. The bay is part of the recreational Mission Bay Park, the largest man-made aquatic park in the United States, consisting of 4,235 acres, approximately 46% land and 54% water. The combined area makes Mission Bay Park the ninth largest municipally-owned park in the United States.