Résumé
A flash flood, which occurred in July 1996 in the Saguenay area (Quebec), transported millions of tons of sediment to the upstream section of the Saguenay Fjord and the Baie des Ha! Ha! in a few days. This first article reports the physical, chemical, and biological observations obtained for the water column in September 1996 and August 1997 and attempts to define indicators that can adequately characterize the effects of the flood on the water column. The chemical composition, the abundance, and the distribution of suspended particles clearly show the influence of the flood on the composition of particles in the water column of the bay and the fjord 2 months and even 1 year after the flood. However, biological indicators such as the abundance and the distribution of phytoplankton and zooplankton species determined in September 1996 are only slightly different between the Bay and the Fjord and show little difference with preflood data. The zooplankton physiological state appears to be a very good indicator of the health of the whole pelagic ecosystem.