The EA explained instead of using standard chainsaws, specialist mechanical equipment would be needed to remove the affected trees.
The machinery would have to be transported to the island by river, adding further logistical challenges.
The agency said additional work would be required to strengthen parts of the island bank before equipment could be brought in.
They said the bird nesting season, which runs from March to September, limited when some work could take place, further complicating the project.
Officials said plans were being explored to restore the island once the dangerous trees have been cleared, adding they hoped to replace the diseased trees with new species better suited to the island’s ecology.
The agency said residents could discuss the plans at a public engagement event on Friday at Staines Library between 14:00 and 17:00 GMT.