The islands of Saint-Ignace-de-Loyola, Dupas and Castors (Beavers) are connected to the north side of St. Lawrence River by a small network of bridges.

The Archipelago of Lake Saint Pierre is a delta from the last glaciation and modified by the alluvium of St. Lawrence River.

[3] Following the withdrawal of the ice cap, the Sorel Islands region was invaded by the Champlain Sea which is then withdrawn gradually, about 12000 years ago.

Today, the same phenomenon is repeated annually during spring flooding[5] while the waters of the river cover a portion of the Sorel Islands and will leave a layer alluvium.

[6] The St. Lawrence River widens the entrance of Lake Saint Pierre which forms a delta archipelago of hundreds of islands and islets.

The disproportion between the contribution of banks is impressive; the report is favourable to ten against one for the south shore to the Archipelago.

[11] Islands and Lake Saint Pierre is the most important migratory stopover in eastern Canada for waterfowl.

The population is concentrated in the Beaver Islands, Dupas, Saint-Ignace and Isle Madame at the north of the Archipelago.

[16] Many summer cottages on pillories were erected along the "chenal aux corbeaux" (Ravens channel), between the Crows and Lapierre Islands.