The Do 28D-2 Skyservant was en route between Machala and Guayaquil, Ecuador at 6000 feet when it entered an area of rainy weather. When 37 miles from the Guayaquil VOR the no. 1 engine lost power and stopped. The pilot continued flight at 600 ft altitude and at a speed of 80 knots. He tried to relight the engine but did not succeed. After entering another area of rain the right hand engine also began to loose power. The pilot was not able to maintain altitude and carried out a forced landing in a river. PROBABLE CAUSE: The possible failure of the left engine (#1) oil pressure pump which led to the abrupt stop of the engine and loss of engine power on the right engine (#2). CONTRIBUTING FACTORS: – Inadequate location to carry out the emergency landing. – Loss of altitude. – Weather conditions present at the time of the emergency. – Failure to perform overhaul to the left engine (#1) oil pressure pump.