In a large, melt the butter on medium heat, when melted, add the celery, onion, garlic, and carrot. Cook for 5 minutes, stirring often.
Add the potatoes, fish, clams, water, salt, and pepper, and bring to a boil then reduce to a low simmer. Cover and cook for about 15-20 minutes or until the potatoes are tender, stir occasionally.
When the potatoes are tender, stir in the milk. Leave on a simmer and cook, stirring often until the chowder is heated through.
Ladle into bowls, sprinkle some black pepper on top, serve with crackers.