Preheat your oven to 350°F (175°C).

In a mixing bowl, combine the chopped chicken, chopped celery, cream of chicken soup, mayonnaise, diced water chestnuts, and slivered almonds.

Mix well.

Transfer the mixture into an ungreased 13 x 9 x 2 inch baking dish, spreading it out evenly.

In a saucepan, melt the butter over low heat.

Once melted, remove from heat and mix in the crushed corn flakes until evenly coated.

Spread the buttered corn flakes over the top of the chicken mixture in the baking dish.

Bake in the preheated oven for 45 minutes or until the casserole is heated through and the top is golden brown.

Serve hot.