* Northeast reservoirs at 29.62 percent capacity * Thermoelectric plants to be kept online for now SAO PAULO, Jan 15 (Reuters) - Reservoirs that fuel hydroelectric plants in Brazil's drought-stricken Northeast recovered slightly after recent rains, data from the national grid operator showed on Tuesday, easing fears of an energy crisis in Latin America's largest economy. Water levels started rising last week in other regions, but in the Northeast, which is suffering its worst drought in decades, they first posted gains on Monday. They were up to 29.62 percent capacity from 29.33 percent. Concerns about an energy crisis mounted during a hot, dry summer in Brazil, pushing up the spot market prices for short-term electricity and raising the possibility of widespread energy rationing for the first time since 2001. Despite recent rainfall and falling short-term energy costs, reservoirs nationwide are still near their lowest levels in a decade. Thermoelectric plants that were activated to avert a crisis will therefore remain turned on for now, the president of the federal energy research institute, EPE, Mauricio Tolmasquim told journalists on Tuesday. But concerns eased as reservoirs in Brazil's densely populated southeast industrial hub rose to 30.43 percent capacity. Energy generated by thermoelectric plants in Brazil was at 11,883 megawatts, according to the grid operator, the ONS. That is a slightly lower burden than had been expected. Brazil relies on hydropower to generate around 67 percent of its electricity, though it has diversified its energy matrix in recent years.