Add half the butter and all the vegetables to a large soup pot over medium heat. Cook the veggies for 5 minutes until they start to soften slightly. Sprinkle the veggies with the Old Bay.
Make a well in the center of the vegetable mixture and add the remaining butter and flour. When the butter melts into the flour, stir in the veggies - they will be sticky once covered in the flour. Let the vegetables cook with the flour for 2 minutes more, then slowly stream in the water and stock, stirring as you go to incorporate the flour.
Let the soup come to a boil and then reduce the heat to simmer, uncovered for 15-20 minutes until the potatoes are cooked through and the soup has thickened slightly. Stir in the clams and cream and let cook for 3 minutes more to heat through.