Shropshire Council, which manages The Mere, says the situation is thought to be improving.
But it says Environment Agency experts will continue to monitor the algae and in the meantime people and their pets should keep out of the water.
Warnings were posted by the council at the end of last month after the algae "bloomed" at both The Mere and Colemere.
An overhead photo taken by a balloonist from Rainbow Hot Air Balloons showed the extent of the potentially toxic bloom.
Only organised swimming is authorised at The Mere and groups that use the water have suspended sessions until the conditions improve.
Traditionally the algae bloom dissipates after a couple of weeks but this year it has been more stubborn.
A spokesperson for Shropshire Council said: “Our partners at the Environment Agency are continuing to monitor the situation at both sites. The latest report from the end of last week is that Colemere is now testing within safe levels.
"The situation at the Mere is thought to be improving, but we would still advise people to stay out of the water and keep their pets from entering it too.”