Distribution and habitat

Hydrodictyon reticulatum, water net, is an invasive species and is considered rare. However erratically water net appears it has been found across the globe.

Although considered rare water net is frequently recorded in rice paddy fields in Asia. In late 1980s to early 1990s  water net had a significant economic and recreational impact in the in the North Island of New Zealand where it appeared for the first time.

Hydrodictyon reticulatum has been found in England for many years but is now spreading north and west. Reports of water net in Dumfries, Scotland and Cork in the Irish Republic have been recieved recently.


Free-floating mats of  often accumulate in vast quantity in sheltered bays along the downwind shores of ponds and lakes. These mats frequently blanket the surface and are capable of undergoing sudden changes in buoyancy and therefore disappear only to quickly reappear especially during calmer periods.

Water net frequently forms extensive surface and subsurface mats in ponds and lakes and in the marginal shallows of rivers during low  flow conditions in the summer months.

Conspicuous seasonal blanketing growths in:

  • Ponds
  • Reservoirs
  • Rivers
  • Streams
  • Ditches
  • Drainage channels
  • Wetlands
  • Patches of damp ground

Water net is often growing attached to the remnants of the filamentous green alga Cladophora.

The rapid spread of water net is attributed to agents such as 

  • wind
  • water movement
  • wildfowl
  • insects
  • livestock
  • humans 

Water net mats generally disappear in September in such lakes and from rivers during the first floods of the autumn.