In a Dutch oven, whisk flour and oil until smooth. Cook over medium-high heat for 5 minutes, whisking constantly. Reduce heat to medium; cook and stir 10 minutes longer or until mixture is reddish-brown.
Add the green pepper, onion and celery; cook and stir for 5 minutes. Add the tomato sauce, water, Worcestershire sauce, garlic powder, paprika, lemon juice and Creole seasoning. Bring to a boil. Reduce heat; cover and simmer for 45 minutes.
Stir in crawfish and heat through. Serve with rice.