Under Mexican law, the guidelines pertaining to all commercial development within a biosphere reserve are straightforward. The development must be a conservation activity, it must maintain cultural values, it must come from or aid the local community, and it must protect the core of the biosphere itself. Rainwater and tidal floods could no longer move nutrients between the salt flats and the lagoon's larger ecosystem. Canals and pump stations would siphon 6,000 gallons of water each second from the lagoon into the concentration ponds, altering the lagoon's currents, threatening larval fish and killing all life sucked into the intake canals. Salt bitterns, a toxic by-product of salt production, would be stored in retaining ponds at the facility before being diluted and released back into the ocean at the lagoon's entrance.
Bitterns contain magnesium sulfate, potassium chloride, bromine, iodine and other toxic compounds.
ESSA's critics fear that heavy rains or breaks in the facility's dikes and retaining walls could release a flood of bitterns into the lagoon. Ships off-loading diesel fuel at the pier could spill toxic fuel, dump trash and discharge bilge water into the otherwise pristine waters outside the lagoon, risking the introduction of exotic species. Numerous toxic spills, ensuing fish die-offs, and pollution became the subject of a 1995 Grupo de los Cien lawsuit charging ESSA with environmental negligence and recurrent violation of Mexican laws. When ESSA began exporting from Guerrero Negro in 1962, gray whales abandoned that lagoon for a decade. This disappearance was undoubtedly caused by ESSA's dredging of the lagoon's mouth to accommodate salt barge traffic.