Two Tree Island was reclaimed from the sea during the 18th century
Two Tree Island near Leigh-on-Sea is set to benefit from a grant of £71,000 for site improvements and surveys.
The 640-acre site has been given the money by Cory Environmental Trust and Veolia Cleanaway Pitsea Marshes Trust.
The grant will be used to improve the habitat for the island's avocets and to monitor other wildlife on the site.
Essex Wildlife Trust has managed the eastern half of the island for 49-years and recently signed a lease to look after the western half as well.
The Trust's Carol Mander told BBC Essex they were now in a position to make several improvements to the island.
One of the main tasks would be to raise some of the avocet's nesting sites to guard against the threat of flooding.
"[We want] to increase the size of some of them and also to make sure the actual top of the island is much better for them for nesting," she said.
Carol was also hopeful the money would help them to get a better understanding of the island's wildlife diversity.
The Island's avocet population has increased markedly in recent years
"We've just started doing a number of surveys which is very exciting," she said.
"It will give us baseline data on the species here, how we can manage them in the future and to monitor the actual work we are doing," she said.
"We've just started to do a reptile survey, we have a breeding birds survey about to start and an invertebrate survey.
"We're also going to do a lagoon assessment which will look at the invertebrates in the lagoon, so it's all very exciting."