Imagine fishermen walking down to the seashore, ready to carry out their early morning routine of preparing their boats and net. 【B1】______ they hope for a good catch of fish. But to their 【B2】______ , a horrible sight meets their still sleepy eyes. Thousands of fish have washed 【B3】______ dead. The cause of this mass destruction? A red tide! Red tides are a global 【B4】______ . They have been observed on both the Atlantic and the Pacific coasts of the United States and Canada. They have also 【B5】______ in many other places. Though relatively few people are 【B6】______ them, red tides are not new. In the Philippines, a red tide was first seen in the province of Bataan in 1908. Since then, red tides have been seen in many other 【B7】______ . A Philippines red tide expert told us that' 【B8】______ the fish kills, the Philippines has documented 1,926 cases of dead shellfish poisoning caused by red tides'. The term 'red tide' 【B9】______ the discoloration of water that sometimes occurs in certain areas of the ocean or sea. Although the color is often red, it may also be 【B10】______ of brown or yellow. The World Book Encyclopedia reports that 'the discolored areas may range from 【B11】______ a few square yards to more than 2,600 square kilometers'. What causes such discoloration? Red tides are generally caused by several 【B12】______ of single-celled organisms. These tiny organisms have hair-like projections which they use to 【B13】______ themselves in water. There are about 2,000 varieties of these organisms, 30 of which carry poisonous 【B14】______ . These minute organisms usually stay in warm waters with high content of salt. A red tide occurs when there is a sudden and rapid 【B15】______ of these organisms. The concentration of these organisms may 【B16】______ to 50,000,000 per quart of water! Although scientists do not fully understand why this happens. It is known that these organisms 【B17】______ when certain conditions simultaneously affect the water. These include abnormal weather, 【B18】______ temperatures, an oversupply of nutrients in the water, a generous 【B19】______ sunlight, and favorable water currents. When a heavy rainfall occurs, minerals and other nutrients are sometimes washed 【B20】______ the land into coastal waters. These nutrients can contribute to the breeding of the organisms. The result? Red tides! 【B1】______