Using open, single-mast wooden fishing boats, whole families are involved with the sea. Once, sponge fishing was a vital industry. Unfortunately, as more people buy man-made, less expensive sponges, the market for natural sponges is dying out. Many Greeks work in the tourist industry. Spectacular historic sites abound on the mainland, while the islands, in particular, draw people from all over the world. In summer, ferries constantly ply the waters among them. Many of the islands have beautiful beaches, picturesque windmills, and snow-white streets. The sun is hot; the sky is clear, sparkling blue. The climate, a combination of Mediterranean and European, affects all three industries- agriculture, fishing and tourism. Athens can be 100 degree Fahrenheit in the shade in July and August. In summer, strong winds cause rough seas, affecting both fishing and ferryboats.