In many regions, wetlands have been filled in so as to be able to use the land for farming. Wetlands are vital for reducing the intensity of floods, as they tend to hold back some of the water. Without wetlands, flood will tend to wash increased sediment and pollutants into the ocean, which can have a detrimental effect on marine life. Coastal developments can also have a negative effect on marine life. The removal or moving of beach sand is in particular damaging to intertidal organisms that depend on specific coastal environments, and rocky shores can be smothered by sand, whereas sand environments can change into bare rocky environments. Impounding of rivers and reduced river flow can result in estuaries becoming closed. Many marine organisms, such as fish, depend on estuaries as nursery areas where they lay their eggs. Reduced opening of estuaries means that many fish species cannot reproduce. Built harbours result in changed currents and alteration of the sea floor, which also disrupts marine ecosystems.
