Situated in the northernmost part of Ontario, just 20 kilometres from the salt waters of James Bay, Tidewater consists of four islands in the Moose River. Here the Artic tides rise and fall twice daily, varying as much as 2.5 metres from high to low.

Vegetation in and near Tidewater is very different from that in the forest areas of the Canadian Shield that lie further south. The boreal forest is somewhat stunted and less dense here because of the northerly latitude and proximity to the tree line. Stunted tamarack, black and white spruce, balsam poplar, trembling aspen and a few white birch grow along the river banks and other well-drained areas. Cranberries, raspberries, willow, tag alder, Labrador tea plant, bog laurel and calypso orchid are all common in the area.

Red squirrel, muskrat and rabbit inhabit the park, and bird life includes grouse, owl, duck and shorebirds. Seals and beluga whales may occasionally be seen in the Moose River.