THE HAGUE – Friday is the last day of opening arguments in the case between Costa Rica and Nicaragua before the International Court of Justice (ICJ) over control of the San Juan River.

Nicaragua argued Thursday that it should regulate the navigation of Costa Rican boats within these border waters.

Costa Rican navigation rights in the river, established in a treaty signed by both countries in 1858, are “limited by certain conditions” that must be set by Nicaraguan regulations, according to Ian Brownlie, professor of international law at Oxford University, who argued in favor of Managua.

The treaty establishes Nicaraguan sovereignty over the river but recognizes Costa Rica's “perpetual navigation rights over commercial objects.” However, the two countries dispute the interpretation of that phrase.

Costa Rica, basing its case in the English translation of the treaty, maintains that the phrase “commercial objects” implies all things with commercial purposes or ends.

Arguing for Nicaragua, professor Antonio Remiro Bretóns, of the Autonomous University of Madrid, said the phrase “commercial objects” must apply exclusively to “articles, cargo or goods that can be traded,” which would exclude the transport of people along the San Juan River, such as tourists.

Nicaraguan authorities prohibited armed Costa Rican police from conducting patrols along the river in 1998. The countries tried to resolve the matter through three years of negotiations beginning in 2002, but when no resolution could be agreed upon, Costa Rica filed a claim against Nicaragua before the ICJ – the United Nation's highest court, at The Hague, Netherlands – in 2005.

Earlier in the week, Kate Parlett, foreign affairs advisor for Costa Rica, argued that the restrictions “have affected the police force's capacity in the fight against drug and human trafficking, especially that of children.”

The two countries will present their final arguments next week, after which the judges will deliberate. It could take several months to hear a ruling in the case.