Union River Bay is a coastal tidal bay located in Hancock County, Maine, serving as the saltwater terminus for the Union River. It offers paddlers expansive views of the Mount Desert Island skyline and hills. The bay connects to larger Blue Hill Bay, providing access to more advanced island circumnavigations. A primary and well-regarded access point for launching is the public boat ramp in Ellsworth, which provides ample parking and leads directly into the tidal Union River. From this ramp, it is approximately 2.5 miles of river paddling before reaching the open vistas of the bay itself. Another documented launch site is a boat landing on Patten Bay in Surry, which provides a more sheltered start before entering the bay's eastern side. The bay is subject to significant tidal influence, and paddlers often plan trips to utilize a rising tide when traveling north from the bay into the Union River towards Ellsworth. Conditions on the bay can change rapidly and are highly weather-dependent. While often calm, winds can funnel into the bay creating rough, choppy seas even when forecasts for surrounding areas are mild. Southwest or east-southeast winds can generate challenging conditions, making exposed crossings potentially inadvisable. Fog is a common and serious hazard, reducing visibility to a quarter mile or less, necessitating the use of navigation tools like charts, a deck compass, and GPS. The area experiences commercial and recreational boat traffic, which should be anticipated, especially when crossing the bay. The water remains open for paddling later into the fall and earlier in the spring than many freshwater bodies in the region, as the tidal flow and power dam runoff delay freezing. Wildlife sightings include harbor seals and loons. For trip planning, paddlers recommend consulting detailed nautical charts and guidebooks such as "Sea Kayaking the Maine Coast" or "40 Kayak Trips on the Maine Coast."