[1][2] The flooding caused by the rapid spring snow melt, coupled with frozen ground, and several heavy rain events that resulted in abnormally high cumulative rainfall for April and May.

[5] During the spring thaw, runoff from snow melt flows into rivers, causing localized overflows each year in many parts of the three provinces.

Most of the reservoirs in the Abitibi-Témiscamingue region were already nearing capacity, and could not hold anymore surplus and the excess water flowed into the Ottawa River and the St.Lawrence River between Mattawa and Gatineau, water levels were expected to rise in the following days to record values[10] Over the following month, the levels in streams began to decline as less precipitation fell and the remaining snow cover was almost all melted away in northern areas and nonexistent in the south.

When the government of Quebec and New Brunswick requested the deployment of the Canadian Armed Forces, approximately 1000 soldiers were first assigned to this task.

The number of deployed quickly rose to more than 2200 after additional assistance in Ontario as well as the added rainfall in late April that continued to raise water levels.