Riga is a Monean. The Monean live under the sea on their ocean planet.
When Voyager visited the planet, the Moneans asked for help, since their ocean was losing containment. Paris and Riga investigated and discovered that eh Monean's mining operations in the ocean was the problem. Riga gave this information to Burkus, a government offical. Burkus said he would included it in report.
Riga decided to do something about the situation and with Paris' help, they tried to disable the mining operations. They were unsuccessful, and Paris was demoted for disobeying Janeway's orders. Riga's efforts to persuade the Monean Government to deal with the problem fell on deaf ears. (VOY: Thirty Days)