The Comité Bandera Azul Ecológica de San Miguel, an environmental organization, is blaming the outbreak of illnesses in a section of Heredia on the lack of action by municipal officials.
Marchers including members of the committee confronted a backhoe operator a month ago near the Río Agra. They said they were surprised Sunday to find a backhoe digging in a wetland near the river.
The Río Agra is the boundary between the cantons of Moravia and Coronado, and a consortium of private groups there have been protesting development work.
Thousands of residents of San Miguel de Santo Domingo de Heredia have been sickened by impure water from the tap. Local schools have been closed and residents marched Tuesday. Municipal officials said that chlorine was left out of the water for two days.
During the rainy season there is a good chance of ground water infiltration into water sources, and the committee blames construction for increasing the run off and also blames the use of agricultural chemicals.
Committee spokesman Nicolas Boeglin said the group presented the concerns in a letter to municipal officials more than a month ago but received no response. They said in the letter in August that the water had a chocolate color.
In addition to possible illnesses from water, the country is experiencing the annual epidemic of stomach flu during the rainy months. Symptoms are similar. Stomach ache, headache and diarrhea.