Spring overbank flooding of the Mississippi River was a major process in the formation and maintenance of the Mississippi delta. Since the early 1900’s, however, most of coastal Louisiana has been hydrologically isolated from the Mississippi River by flood control levees. As a restoration effort, a diversion structure was constructed at Caernarvon, approximately 30 km down river from New Orleans, which allows water from the Mississippi River to pass into the Breton Sound estuary. The estuary consists of about 1100 km2 of fresh to brackish wetlands. This study focuses on the effect on water quality in the Breton Sound estuary from a large ‘pulse’ of water intentionally let through the structure in the spring of 2001. The pulse had a peak discharge of 220 m3/sec1, and was sustained for 14 days. The pulse had a profound effect on salinities throughout the Breton Sound estuary. Based on salinity responses in the basin, water residence time in the estuary was between one to two weeks. Suspended sediments were rapidly deposited in the estuary within the first several km of the diversion structure. The estuary was an effective sink for nitrogen and phosphorus, with a 47% decrease in NO3+NO2; 44% decrease in total nitrogen; 16% decrease in phosphate; and a 48% decrease in total phosphorus in the upper half of the estuary. These results imply that river diversions may be used to process Mississippi River water prior to reaching offshore waters where eutrophication has become a recent concern, as well as enhancing marsh formation and stability, and preventing salt water intrusion from degrading Louisiana's remaining coastal wetlands.