THE mosquito-infested jungle near the mouth of the San Juan river seems of little value. But to Daniel Ortega, who in a year’s time plans to seek a third, unconstitutional, term as president of Nicaragua, the sticky marshland is proving useful. The right bank of the river marks Nicaragua’s border with Costa Rica. The two countries have squabbled over navigation rights for more than a century. But last month Nicaragua went further: a group of Nicaraguans dredging the river set up camp on the Costa Rican side, backed by about 50 soldiers. That prompted Costa Rica to send 70 police to the border and to call in the Organisation of American States to mediate (it wants both sides to withdraw and talk).