Creamy Seafood Chowder

Name: Creamy Seafood Chowder
Ingredients: 4 tablespoon(s) butter and/or olive oil, divided; 1/2 cup(s) onion, diced; 1/2 cup(s) celery, diced; 3 clove(s) garlic, minced; 1 1/2 teaspoon(s) oregano, divided; 1 pound(s) medium raw shrimp, cleaned; 1 pound(s) scallops; 1 pound(s) cod filets, broken into chunks; 2 cup(s) hot water; 2 teaspoon(s) chicken boullion; 2 cup(s) half and half, fat free; 2 cup(s) milk, skim; 2 tablespoon(s) corn starch; 2 teaspoon(s) Old Bay seasoning; 3 medium thin skinned potatoes (I used golden)