Data represent physical (water quality, water nutrient analysis) and biological (fish, macroinvertebrate, and vegetation community) collections from the Shiawassee National Wildlife Refuge in Saginaw, MI, USA (specifically, historical management unit "Pool 1A" and the North and South management units of the Maankiki Marsh Complex.) The North and South management units of the Maankiki Marsh Complex were reconnected to the Shiawassee River in 2018, whereas Pool 1A represents a historically reconnected wetland. Additional sites within the Shiawassee River and Spaulding Drain (east of Pool 1A) were also sampled to represent parameters collected from the parent water system. All data were collected in 2019.