A series of focused field programs took place within Hudson Bay during 2017 to provide a time series of winter and summer observations in Hudson Bay. The first of these field programs was a winter survey of the Churchill River estuary and mobile ice pack offshore from Cape Churchill in Southwestern Hudson Bay. Nine participants from four of the five teams that comprise BaySys spent two weeks in Churchill to conduct in situ sampling of the ice and underlying water column, while also deploying an array of autonomous equipment to collect a longer temporal dataset of key variables both in the estuary and in the mobile ice pack. Scientists stayed at the Churchill Northern Studies Centre (CNSC) who provided snowmobiles for the estuary sampling (Sites in Figure 1), while two A-Star helicopters form Great Slave Helicopters were used to access the offshore ice pack.