Original sentence: In 1178, they launched a surprise attack on the Khmer capital by sailing a fleet up the Mekong River, across Lake Tonle Sap, and then up the Siem Reap River, a tributry of the Tonle Sap
Edited sentence: In 1178, they launched a surprise attack on the Khmer capital by sailing a fleet up the Mekong River, across Lake Tonle Sap, and then up the Siem Reap River, a tributary of the Tonle Sap