North Killingholme Haven Pits SSSI is near Immingham, North East Lincolnshire, on the south bank of the Humber Estuary (central grid reference TA1662919816). The privately owned,16ha, site comprises former clay pits which have developed into saline lagoons. It is within the Humber Estuary Special Protection Area/Ramsar site and is of international importance for non-breeding waterfowl. The site is connected to the Humber Estuary by a manually operated sluice in the flood bank, which allows for the regulated exchange of tidal water. The sluice is over 50 years old and is not fully functioning due to siltation, and health and safety concerns regarding its operation. The aims of the investigation are to assess the existing sluice, and appraise the options for management of water levels to achieve the site objectives. Outputs include concept designs and estimated costs. A site visit is required to understand the site and the constraints, and assess the existing sluice. (Note this opportunity was first published in July 2025 but a contract was not awarded. This is a re-publishing with a revised specification and increased estimated maximum value)