The workers were seen on Pelham Beach during the weekend and are carrying out work on behalf of Southern Water.
The outfall pipe drains water into the sea and is believed to have become blocked with shingle.
Engineers were seen lengthening the pipe on behalf of Southern Water.
A spokesperson for Southern Water, said: “We’re in the process of improving a surface water outfall pipe at Pelham Beach. The works will protect the pipe and prevent it from being blocked by shingle.
“We recognise this scheme may have an impact on beach users, so we will provide regular updates. We’re sorry for any inconvenience caused during this important work.”
Engineers were seen lengthening the pipe on behalf of Southern Water.