was it used for navigation?
The river as far as Stamford was used by the Romans for navigation, as it formed part of a system including the Car Dyke, which ran along the western edge of the Fens and crossed the river near the modern Folly River.
River Welland
The river as far as Stamford was used by the Romans for navigation, as it formed part of a system including the Car Dyke, which ran along the western edge of the Fens and crossed the river near the modern Folly River. 
where does the river welland start and finish The river 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 can we see any wild animals there? It provides habitat for stone loach and bullheads.
wiki:1154797
River Welland [SEP] Navigation
The river as far as Stamford was used by the Romans for navigation, as it formed part of a system including the Car Dyke, which ran along the western edge of the Fens and crossed the river near the modern Folly River. Navigation to Stamford was improved by the canal. Boats used on the canal were small lighters, around wide, capable of carrying from seven to fourteen tons, and normally worked in trains of four vessels. With the arrival of the railways, river trade declined. The Midland Railway reached Peterborough in 1846, and opened their line to Melton Mowbray, passing through Stamford, in 1848.