Natural England (NE) Survey of Humberstone Fitties Lagoon dataset https://portal.medin.org.uk/portal/start.php?tpc=010_13ac25a30a30cef6dc086e68adf96d8e Previous surveys have revealed that Humberstone Fitties Lagoon has a rich community comprising many lagoon specialist species. It is the most northerly site in Europe for Gammarus insensibilis an amphipod protected under schedule 5 of the Wildlife and Countryside Act 1981. It is known that Gammarus insensibilis is reliant upon the alga Chaetomorpha linum for which this is the most northerly English site. This survey was carried out, between May and September 2001, to assess the current status of the lagoon community with particular emphasis on the population of Gammarus insensibilis. Previous studies had also reported the loss of Hydrobia ventrosa, which has now been re-found in large numbers. There was also confusion over the identity of bryozoan present in the lagoon, which was confirmed to be Conopeum seurati and the presence of a Cockle species Cerastoderma, which was found to exist only as dead shells and should not be considered part of the lagoon fauna. The lagoon was found to be in good condition with the discovery of five new species and the rediscovery of one that was previously lost. Two species that had been previously recorded were not found in this study, Polydora ciliata and Caulleriella (zetlandica), the former may well be extinct as the site no longer appears to support its habitat requirements, the latter may persist in small numbers and may have been missed. It was notable that this was the first time fish have been reported in the lagoon with two species now appearing to be established, further monitoring may be required to determine their impact on the lagoon. Humberstone Fitties Lagoon was found to contain abundant dense submerged vegetation composed of Chaetomorpha linum and Ruppia maritima; between they occupied most of the lagoon with Ruppia favouring shallower water than Chaetomorpha. The water level and salinity of the lagoon was observed to fluctuate over the course of the year in an expected natural pattern. High spring water levels were followed by a decrease with a corresponding salinity increase due to evaporation over the summer until the site flooded on the spring tides in autumn. No water is taken on over summer as the lagoon has no direct connection to the sea only tides high enough to overtop the banks are sufficient. The lagoonâ??s salinity was found to vary from 11 0/00 to 24 0/00, which is the preferred range of most species present. Four saltmarsh pools border the main lagoon, which experience drying out and hypersalinity during the summer and so support impoverished fauna. There is evidence however that one of these pools may now be subject to more regular tidal inundation resulting in more favourable conditions and may be developing into a lagoon. Many of the individuals present in this pool do show signs of tidal stranding and so this pool requires monitoring to determine its true nature. The threats facing the lagoon are discussed and management to prevent them and to maintain the general condition of the lagoon are discussed. 20211101