It inhabits lowland fen and grazing marsh areas and is dependent on the presence of standing or slow moving neutral to alkaline water.

Emergent vegetation is highly important for use as perches for hunting and basking and to support nursery webs.

They are also known to hunt underwater by running down the stems of plants to reach prey, this can also be used to avoid capture by predators.

Courtship and mating usually takes place early in the season and adult males will die shortly after with most dead by late July.

[7] Populations of the great raft spider are found throughout Europe and Russia,[2] in Austria, Belarus, Belgium, Bulgaria, Czech Republic, Denmark, Estonia, Finland, France, Georgia (country), Germany, Hungary, Italy, Latvia, Lithuania, Norway, the Netherlands, Poland, Romania, Serbia, Slovakia, Sweden, Switzerland and the United Kingdom.

[1][8][9] In 1956 an outlying population was discovered for the first time in the United Kingdom at Redgrave and Lopham Fen by arachnologist Eric Duffey.

A further two populations have since been identified at the Pevensey Levels in East Sussex by Peter Kirby in 1988 and near Swansea, South Wales, by Mike Clark in 2003.

[12] The lack of historical record makes it very difficult to estimate the extent of its decline or explain the widely separated current distribution in the UK.

Although the species is widely distributed in Europe, under-recording and confusion over identification make assessment of its status difficult.

To maintain the density and range of the fen raft spider on the Pevensey Levels and to introduce populations to two suitable new sites by 2010.

However, water extraction from the nearby borehole and a series of droughts in the 1980s reduced the population to only two isolated areas on the reserve.

The removal of the borehole in 1999 was expected to trigger an increase in population as water levels returned to normal.

The population of the fen raft spider at the site remains small and restricted in distribution, but stable.

[16] A second population, which had previously been believed to be the similar Dolomedes fimbriatus, was identified in 1988 at the Pevensey Levels in East Sussex.

[18] Surveying found a stable population as well as identifying further occurrences at the nearby Crymlyn Bog and in connecting wetlands[11] but the full range of the spider is not fully known.

[20] The project saw around 3000 spiderlings bred and reared by Dr. Helen Smith and the John Innes Centre, 1600 of which were released into suitable dykes at the Suffolk Wildlife Trust Castle Marshes nature reserve.

The site is part of the Suffolk Broads and lies 50 kilometres (31 mi) downstream, from Redgrave and Lopham fen, between Lowestoft and Beccles.

Work was carried out to improve the ditch network at the site to prepare for the reintroduction and provide optimal habitat for the new spider population.