Melt butter in a large non-stick pan over medium heat.

Add chopped celery, onions, and green bell pepper to the pan.

Saute the vegetables until they become soft and translucent.

Add chopped garlic and bay leaves to the pan.

Saute for an additional 1-2 minutes, until fragrant.

In a separate bowl, dissolve flour in water until smooth.

Pour the flour-water mixture into the pan with the vegetables.

Cook for 10-12 minutes, stirring constantly, until the sauce thickens.

Add crawfish tails and cayenne pepper to the pan.

Stir well to combine and cook for 5 minutes, allowing the crawfish to heat through.

Add chopped scallions and parsley to the pan.

Cook for 3-4 minutes more, until the herbs are wilted and incorporated.

Serve hot over rice.