The Fronsac Lake (French: Lac Fronsac) is a freshwater body located in the unorganized territory of Lac-Pikauba, in the Charlevoix Regional County Municipality, in the administrative region of Capitale-Nationale, in the province of Quebec, in Canada. This body of water is located in the Laurentides Wildlife Reserve.

Lake Fronsac is one of the head water bodies of the Malbaie River. This mountain lake is entirely located in an area where forestry has always been the predominant economic activity. In the middle of the 19th century, recreational tourism activities took off. Due to the altitude, this lake is normally frozen from the end of October to the end of April; however, the safe ice circulation period is usually from early December to April.

Secondary forest roads serve the southern part of the hydrographic side of Lake Fronsac. Another motorable road serves the northern part. The northeast part has no road.

Located in a forest zone in the unorganized territory of Lac-Pikauba in the Laurentides Wildlife Reserve, the lake Fronsac (length: 2.2 kilometres (1.4 mi); altitude: 821 metres (2,694 ft)) is located on the western slope of the Malbaie River valley. The mouth of Fronsac Lake is located on the east side of the lake and is open onto lac à Jack. This mouth is located at:

• 3.1 kilometres (1.9 mi) west of the mouth of lac à Jack;
• 3.67 kilometres (2.28 mi) north-west of the mouth of the Lac à Jack outlet (confluence with the Malbaie river);
• 4.3 kilometres (2.7 mi) north-west of a bay in Malbaie Lake;
• 43.9 kilometres (27.3 mi) west of downtown Baie-Saint-Paul;
• 65.9 kilometres (40.9 mi) south-west of La Malbaie town center.

From the mouth of Lake Fronsac, the current crosses 3.1 kilometres (1.9 mi) to the east at Lac à Jack; then descend on 2.1 kilometres (1.3 mi) to the south the outlet of the lake at Jack; from there, the current follows the course of the Malbaie river on 148.9 kilometres (92.5 mi) with a drop in level of 818 metres (2,684 ft) which pours into La Malbaie in the St. Lawrence River.

The term "Fronsac" turns out to be a commune in the southwest of France, located in the department of Gironde. The name appeared on the draft of the Jacques-Cartier Lake map, 1959-11-04, item 81. "Lac à Loutre" is a variant of the official name.

The toponym "Lac Fronsac" was formalized on December 5, 1968 at the Place Names Bank of the Commission de toponymie du Québec.

• Charlevoix Regional County Municipality
• Lac-Pikauba, an unorganized territory
• Laurentides Wildlife Reserve
• Zec des Martres
• Lac à Jack
• Malbaie River