The Sainte Marguerite-3 (SM-3) Complex is among the largest hydroelectric projects in eastern Canada. The Complex is located some 90 km from the mouth of the Sainte-Marguerite River, a 280 km long river that empties into the St. Lawrence River near Sept-Îles, Quebec. Two small privately owned power stations are located near the river mouth: Sainte-Marguerite-1 (8.5 megawatt (MW)), which belongs to Hydrowatt, and Sainte-Marguerite-2 (18 MW), operated by Gulf Power. To meet Quebec’s energy needs, Hydro-Québec started building an 882 MW hydroelectric generating station on the Sainte-Marguerite River in 1994. The works include a 171 m high earth and rockfill dam, a three-gate spillway, an 8 km headrace tunnel, and a two-unit underground power-house. Construction of the dam required the excavation of a 900 m long diversion tunnel and the construction of an upstream cofferdam. The project develops a total hydraulic head of 330 m, of which ~180 m are in the 13 km of rapids from the dam toe to the powerhouse tailrace. Filling the reservoir started in the spring of 1998 (i.e., before the dam construction was finished) and was completed in the autumn of 2002. A 140 km long reservoir was created with a depth of 120 m near the dam toe. The reservoir follows a jagged course and its width varies from a few hundred meters to 10 km over its length. The project was completed in 2002 and power generation started in 2003. This paper discusses the issues surrounding the creation and solution of a 3-D finite element numerical model based on a compilation of field data from various sources. The creation of a successful finite element mesh utilizing actual field data is presented. Results are discussed in relation to numerical modeling in 2-D carried out in the traditional manner. Recommendations for future flow numerical modeling of these types of 3-D structures are discussed.