Several hundred people protested on a beach in Telde on Sunday against offshore fish-farming activities near the coastline.
Demonstrators gathered on land and in the water, using kayaks and swimming toward fish-farming cages to denounce alleged marine pollution.
Protesters say intensive sea bass farming has caused repeated pollution incidents, leading to beach closures in recent months.
Local residents and environmental groups called for the removal of the cages, while the mayor said authorities are seeking measures to prevent further contamination and ensure public safety.