The Tullahan River (running between the cities of Caloocan and Valenzuela) turns pink and purple as foam from unknown source covers part of the river. People living in the area say that the formation of effluent in different colors occurs almost everyday. Residents along Tullahan river have noted a multi-coloured effluent in the river water, rocks and banks. Several industries, such as paper, pen and dye factories, are located upstream from this site.