Leigh Day said anyone who had been affected by sewage spills was eligible to join the legal action.
It said the claim was launched in 2024 after separate legal action taken by keen swimmer Jo Bateman from Exmouth.
The retired physiotherapist, whose claim is ongoing, said swimming benefitted her physical and mental health but frequent sewage spills on her local beach prevented her from entering the water.
The firm said so far more than 1,400 people who argued pollution had negatively impacted businesses, many of which rely on tourism, had joined the claim.
It argued “SWW’s failings were wide and entrenched in many coastal towns across the Devon and Cornwall region”, not just the Exmouth area, and it highlighted a 2025 investigation by water regulator Ofwat into its mismanagement of wastewater treatment works and sewer networks.