Water quality could be monitored to ensure the safety of fish and other river wildlife if a second Tyne Tunnel is built.
A public inquiry at Jarrow into the proposal for a new tunnel heard that during construction, water could be monitored at 15-minute intervals for oxygen levels, water turbulence, temperature, salt content and speed.
If alarms were triggered, work would stop and would only re-start when conditions returned to pre-set target levels.
Dr Paul Johnson, a director of consultants Arup, said that because the Tyne is recognised as the best salmon river in England, dredging for the new tunnel would be restricted to between November and March to minimise impact on fish migration.
It is also proposed to continuously monitor existing water quality near the Jarrow to Howdon crossing point for at least two years prior to dredging.
The inquiry continues.