The Lake presumably drains into the (unnamed) river at the Foot of the lake. Captain John sees from the charcoal-burners' camp: Away to the south the lake narrowed and narrowed until it became a winding river through green lowlands. A little cloud of white steam where the lake ended and river began showed showed where one of the lake steamers was resting by the pier there (SA13).
Sammy the policeman rows to the island and says I've got to row right down to the foot of the lake (SA24).
The hounds on a practice trail that run through the camp are from Low End, and start near the steamer pier. They hear the finish at the foot of the lake, a noise of yells and rattles and shrill whistles and screams and howls .... like parrots and monkeys all yelling together (SD17).
Mary Swainson goes from the Rio Station,because going from the station at the Foot of the Lake she would have had to change twice and travel all round the estuary (PM23) rather than with no changes from Rio. And the Great Aunt would not have gone from there either with all the changes (PM25).
There is a steamer pier, as the Ds are passed by a big steamer, her decks crowded with passengers, going on her way from Rio to the foot of the lake, and are thrown all ways by her wash (PM20).
The town of Lakeside at the foot of Windermere, with the Lakeside & Haverthwaite Railway (now an isolated tourist line but originally connected to the British railway network) resemble Foot of the Lake and its rail connection around the estuary.