To measure the effectiveness of runneling in the Parker River National Wildlife Refuge (PRNWR), baseline assessments of hydrology, vegetation, water chemistry, and avian biodiversity were conducted in 2020 and 2021. In 2020, seven study sites were identified on Plum and Pine Island, consisting of three sites to be runnelled, two sites designated as no- action control sites, and two sites that naturally breached (Figures 1a and b). For comparison of the hydrology of natural pools to the other sites, two small, natural pools were selected (Figures 1b). At each runnel, control, and natural breach site, two 50m transects were run along the pool edge on opposing sides. Five locations along each transect were selected by a random number generator and a 0.5m2 quadrat (plot) was placed on the marsh platform and then flipped into the pool. Within each plot, visual percent cover of vegetation by species was estimated and a water sample was drawn using a sipper and preserved in a zinc acetate solution to be later tested for sulfides. In the field, water samples were also analyzed for salinity (ppm) and redox (Eh). For hydrology assessments, pressure transducers (Onset, Model U20L) were used as water level recorders (WLRs) and housed in PVC cases and mounted to fenceposts set in creeks (2) and pools (9) at each of the nine sites. To account for avian presence and diversity, point counts were conducted at each site: once in 2020 and twice in 2021. Although saltmarsh sparrows were the primary species of concern, all birds observed or heard in a five- minute period within a 100m radial plot in each treatment area (3 runnel, 2 control, and 2 natural breaches) as well as the megapool located on Refuge Road on Plum Island were recorded.