The first is on the north side of the river in Colney Heath Local Nature Reserve .
Is a square - section cast iron pillar made by Henry Grissell at his Regents Canal ironworks and erected in 1861 or 1862 .
The first is on the north side of the river in Colney Heath Local Nature Reserve , and is a square - section cast iron pillar made by Henry Grissell at his Regents Canal ironworks and erected in 1861 or 1862 .