The rapid growth of the Billingham site showed itself in the need for more land. It had taken nearly 25 years before it outgrew itself and Wilton was created on a much larger site on the South bank of the Tees. Only 15 years later more space was needed and work began on the north bank of the Tees estuary at Seal Sands, home to a mass of seals and sea birds. In spite of the massive industrial developments, the needs of the seals and the birds have still been looked after. 
Picture Stockton Archive
A Pictorial History of Stockton-on-Tees
Presumably the dark wavy line in the left hand corner is Lustrum Beck. At this point it used to be highly polluted as the area on the lower left used to be the Corporation waste tip.
This is not the Wilton Site but Billingham – looking North from Portrack Lane towards Haverton Hill Road. The roundabout is now covered by the Tees flyover.
This view is of Portrack Lane and industrial estate to the lower left and Portrack roundabout in the centre. River tees is to the right and ICI Billingham in the upper centre.