Image description: Shoals of juvenile salmon, known as smolts struggling with barriers in the River Itchen. Image by Kieran Gillingham.
The Environment Agency and partners are looking for ways to improve fish passage past barriers and restore the lower River Itchen by Southampton.
Each spring, shoals of juvenile salmon, known as smolts, begin their journey to the sea. This journey begins on the River Itchen, through the estuary, and out to the sea where the salmon feed and grow before returning to the river as adults to spawn. But salmon are struggling to get past barriers in the river during their journey to the sea. The bottom section of the River Itchen where it transitions to the estuary has been changed many times historically. It was once used for transport and trade as a sea lock and onward travel to Winchester. Now, the current structures control water levels through Riverside Park. These structures present the biggest obstacles for smolts, especially in large groups. The sharp change in water velocity created by these structures causes smolt to become hesitant and bunch up, making them vulnerable to predation and poaching.
The situation for smolts is further complicated by issues upstream in Riverside Park, where the manmade channel sits higher than the natural floodplain. Gravity has caused the river to ‘breach’ – meaning a significant amount of water is now branching off from the main river and finding its own natural course through the floodplain. For now, this does not affect the smolt who continue to follow the main course of the river, ignoring any offshoots. But over time this breach will take more water and impact the ecology of the river downstream.
In response to these intertwined issues, the Environment Agency has launched a study to find options to help smolts and improve the lower River Itchen chalk stream and wetland system.
Water abstraction threatens River Itchen
On the River Itchen, the impact of record water abstraction, revealed by the Guardian and Water Investigations, is already showing. In 2022 and 2024, returning adult salmon numbers hit the lowest and third lowest levels ever recorded, just 133 and 187 fish respectively. If another drought hits, the river and its endangered salmon could be pushed to the edge.