The document discusses hypoxia in estuaries caused by excess nutrients leading to increased phytoplankton growth and decreased dissolved oxygen levels. It notes that nitrogen is usually the limiting nutrient in oceans and estuaries. During periods of thermal stratification in spring and summer, low oxygen water is trapped on the bottom, causing hypoxic conditions harmful to marine life. Solutions proposed include upgrading sewage treatment plants, reducing agricultural and urban runoff, limiting fertilizer use, and decreasing phosphates in household products.