For a long period of time relationship between Costa Rica and Nicaragua were characterized by conflict. These circumstances resulted in a considerations of problematic issues by international agencies, such as the International Court of Justice, Organization of American States.
For instance, in 1998, when Nicaragua banned transit of Costa Rican police vessels on the river, it was considered it to be infringement of sovereignty, and unilaterally introduced a 25 USD $ tax for any Costa Rican tourists coming to San Juan River, as the persons were not the objects of trade but the subject of trade and, therefore, were not subject to the existing agreements of free movement along the river. This case was adjudicated by the International Court of Justice, and the key points of this judgement are as follows:
As to the Costa Rica navigation rights over San Juan River in accordance with the Treaty of 1858: Costa Rica has the right to free commercial navigation along the San Juan River, including passenger and tourist transportation. People travelling San Juan River on Costa Rican vessels, exercising the right of Costa Rica to free navigation, should not get Nicaraguan visas or buy tourist cards. Costa Rica does not have the navigation rights over San Juan River for vessels performing police functions.
With regards to the right of Nicaragua to regulate navigation on San Juan River in the area where the navigation is of general character: Nicaragua has the right to demand from Costa Rican vessels and their passengers to stop at the first and last Nicaraguan posts along their routes.
With regards to the natural fishery: fishing by the Costa Rican residents of San Juan River area to ensure their subsistence should be considered by Nicaragua as customary law;
Nicaragua does not act in accordance with its obligations with regards to the Treaty of 1858, when it demands from people travelling San Juan River by Costa Rican vessels, exercising the right of Costa Rica to free navigation, to get Nicaraguan visas.
However, it is more interesting from the point of environmental law to consider resolution of these cases related to certain measures taken by Nicaragua in transboundary region (Costa-Rica vs. Nicaragua), and road construction in Costa Rica along the banks of San Juan River (Nicaragua vs. Costa-Rica).