'Lincolnshire Fenland Lidar' by Steve Malone — fabulous images of ancient watercourses in the Witham valley and Lincolnshire Fenland https://academia.edu/5807526/Lincolnshire_Fenland_Lidar

The Witham valley in Lincolnshire from Bardney to Billinghay, showing previous reconstructions of the marine incursions and dendritic creek systems here vs that shown by Lidar: https://academia.edu/5807526/Lincolnshire_Fenland_Lidar

It has been argued that the River Witham & multiple causeways across its valley were used for votive deposition from the pre-Roman era right through to the 14th century; items recovered including the Iron Age 'Witham Shield': https://books.google.co.uk/books?id=4YKrpH222eYC&pg=PA271#v=onepage&q&f=false & https://research.britishmuseum.org/research/collection_online/collection_object_details.aspx?objectId=831234&partId=1&searchText=witham&sortBy=imageName&page=1

A 2,500 year old Iron Age boat from the Fiskerton causeway across the River Witham, Lincolnshire; now in
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Stake from the Fiskerton causeway across the River Witham, Lincolnshire, dated by dendrochronology to 436-405 BC, in
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A 7th-century Anglo-Saxon 'sugar-loaf' shield boss found in the River Witham, Lincolnshire, in the late 18th century.

The late 8th-century Witham Pins, found in the River Witham, Lincolnshire, in 1826; a probable ritual deposit: https://research.britishmuseum.org/research/collection_online/collection_object_details.aspx?objectId=85827&partId=1

Detail of the late 8th-century Witham Pins: http://medieval-illumination.blogspot.co.uk/2013/01/anglo-saxon-treasure.html

The 8th-century 'Witham Bowl', likewise recovered from the river, had a similar creature rendered in 3D :) Found at Washingborough in 1816, now sadly lost...

A Viking axe found in the River Witham, Lincolnshire; in
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The 9th-century Fiskerton Sword, found on the north bank of the River Witham, Lincolnshire, in 1954 by a boy, presumably after dredging. The sword is 90cm long and is decorated with Trewhiddle-style silver mounts inlaid with niello.

A 10th-century sword recovered from the River Witham opposite Monks' Abbey, Lincoln; the sword bears the inscription + LEUTLRIT and 'is of continental manufacture, while the hilt-fittings would have been added by an Anglo-Saxon craftsman': https://www.britishmuseum.org/collection/object/H_1848-1021-1