The southern outfall works of the London main drainage system are at Crossness in the neighbouring lowland called Plumstead Marshes.
Nine or ten miles before reaching its outfall the river enters St Petersburg, and 5 or 6 m.
From here to its outfall in the China Sea the river winds for some 400 m.
There are actually two distinct systems, north and south of the Thames, having separate outfall works on the north and south banks of the river, at Barking and Crossness.
Issuing from the lake within Nicaraguan territory, the San Juan has a course of 95 m., mostly along the frontier, to the Colorado Mouth, which is its main outfall, and belongs wholly to Costa Rica.
The existence of ancient lacustrine beaches, upheaved between the two basins by volcanic agencies or left dry by some enlargement of the San Juan outfall, and a consequent subsidence of the water-level, seems to indicate that the lakes were formerly united.