Orillia is located on the shores of two connected lakes: Lake Simcoe and Lake Couchiching. Both lakes are part of the Trent-Severn Waterway. Travel north on Lake Couchiching, then through three locks and the only marine railway (Big Chute Marine Railway) still in use in North America leads to Georgian Bay on Lake Huron. Travel south-east across Lake Simcoe, through many locks (including two of the highest hydraulic lift locks in the world, Peterborough Lift Lock and Kirkfield Lift Lock) eventually leads to Lake Ontario. From either of these Great Lakes one can connect to the St. Lawrence and thence to the Atlantic Ocean.