Pennsylvania has three major rivers - the Ohio, Susquehanna, and Delaware Rivers. It also has several reservoirs and lakes, including Allegheny and Pymatuning reservoirs in the northwest and Raytown Lake in the south. Over 1,239 square miles of Pennsylvania are covered by water, including Lake Erie which is the largest lake in the state. Greenhouse and nursery products as well as mushrooms are top agricultural crops, while livestock - especially milk from dairy cattle - also contribute significantly to Pennsylvania's economy. The cities of Philadelphia and Pittsburgh have historic buildings and sites from the American Revolution and are known for foods like cheesesteaks and as the former steel capital of America.