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The River Welland is a river in the east of England, some 65 miles long. It rises in the Hothorpe Hills, at Sibbertoft in Northamptonshire, then flows generally northeast to Market Harborough, Stamford and Spalding, to reach The Wash near Fosdyke. For much of its length it forms the county boundary between Northamptonshire and Leicestershire, Rutland, Lincolnshire and Cambridgeshire. It is a major waterway across the part of The Fens called South Holland, and is one of the Fenland rivers which were laid out with washlands. There are two channels between widely-spaced embankments with the intention that flood waters would have space in which to spread while the tide in the estuary prevented free egress. However, after the floods of 1947, new works such as the Coronation Channel were constructed to control flooding in Spalding and the washes are no longer used solely as pasture, but may be used for arable farming.

The Environment Agency is the navigation authority for the river, which is navigable as far upstream as Crowland, and with very shallow draught to West Deeping Bridge. The lock around the weir there is not usable. The traditional head of navigation was Wharf Road in Stamford. The management of the lower river has been intimately tied up with the drainage of Deeping Fen, and the river remains important to the Welland and Deepings Internal Drainage Board, for whom it provides the final conduit to the sea for pumped water. It is tidal as far upstream as Fulney Lock (from Wikipedia).

King Street is the name of a modern road on the line of a Roman road (Margary Road number 26). The road left Ermine Street near Peterborough (Durobrivae) and then ran north for about 30 miles, close to the edge of the Fens, to rejoin Ermine Street at Ancaster (possibly Causennae).
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The Fens, also known as the Fenland, is a naturally marshy region in eastern England. Most of the fens were drained several centuries ago, resulting in a flat, damp, low-lying agricultural region.
A fen is the local name for an individual area of marshland or former marshland and also designates the type of marsh typical of the area, which has neutral or alkaline water chemistry and relatively large quantities of dissolved minerals, but few other plant nutrients.
Fenland primarily lies around the coast of the Wash; it reaches into four counties: Lincolnshire, Cambridgeshire, Norfolk and a small area of Suffolk, as well as the historic county of Huntingdonshire. In whole it occupies an area of nearly 1,500 sq miles.
Most of the Fenland lies within a few metres of sea level. As with similar areas in the Netherlands, much of the Fenland originally consisted of fresh- or salt-water wetlands, which have been artificially drained and continue to be protected from floods by drainage banks and pumps.