A small ditch dug by Nicaragua across Costa Rican territory is an environmental time bomb, according to those who live near the river.
They expect the Río San Juan to blast through the ditch at the next flood and create a new mouth for the river that now meanders to the Caribbean.
The environmental organization Preserve the Planet also has expressed its concern about the Nicaraguan activities in the Refugio de Vida Silvestre Barra del Colorado.
So far, Costa Rican officials seem to be dwelling on the diplomatic and have given scant notice to the looming environmental disaster.
Among the possible consequences is a drastic drop in the water level of the now navigable Río Colorado that flows from the Río San Juan to the Caribbean. There is world-class tarpon fishing there, and the fish appear to use the Río Colorado for mating runs upstream.
Some Barra del Colorado residents are concerned that Nicaraguan activity will disturb or destroy adjacent lagoons which appear to be the locations where tarpon fry grow large enough to challenge the sea.
Preserve the Planet also noted that the area where Nicaragua has invaded Costa Rica is part of the San Juan La Selva-El Castillo biological corridor, which is itself part of the larger mezoamerican corridor.
The organization noted that it has worked for several years to protect the corridor. It called for the Nicaraguan troops to go home.