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 such as milk, beef, and chickens also contribute significantly to Pennsylvania's economy. The climate varies across the state with cold winters and temperatures ranging widely by region.