Cut the salmon into pieces and lightly dredge with flour.
Roll out each of the pie crusts, slightly thicker than normal.
Cut salt pork into thick strips and spread evenly in the bottom of a 2 qt. casserole dish. Arrange half the salmon on the salt pork. Sprinkle with half of the celery, onion and potato slices; season with salt and pepper.
Cover potato layer with one of the pastry dough, cutting two slashes in the dough to 'vent' the dish. Pour in water through the vents until level with the pastry.
Layer with the remaining fish, celery, onion, potato and season with salt and pepper. Cover with top pastry crust and again cut out two vents. Pour water in vents until level with pastry.
Bake uncovered in a preheated 350°F oven for 1 1/2 hours or till crust is golden-brown.