If care is not taken large scale coastal developments can directly remove the seagrass or smother it.
Coastal pollution by sewage or chemicals can cause the seagrass to be smothered by algae or directly poisoned.

• People also damage the seagrass by:
• Mooring in it – as anchors pull up roots, allowing storms
  and currents to wash away large areas
• Travelling at high speed over it – as boat propellers and keels,
  and jet ski jets can cut through the leaves and roots scarring
  and killing the seagrass
• Discharging waste and rubbish over it – as waste in the water
  cuts out light and  allows algae to smother the seagrass
• Fishing with scallop dredges and other mobile fishing gear
  through it – as dredges breaks up the seagrass bed
• Using gill and tangle nets – as anchors and footropes can
  pull up the seagrass
• Walking on the seagrass – as this tramples the plants and
  breaks off  the leaves