In late 2018, we were commissioned by AECOM to provide marine mammal mitigation services during hydrographic surveys of the River Thames. We provided an experienced team of Marine Mammal Observers (MMO) and Passive Acoustic Monitoring (PAM) operatives to ensure 100% coverage during hydrographic operations. The programme of works involved the provision of expert advice and the development and implementation of a bespoke set of procedures to mitigate any injury or disturbance to a Beluga whale (known as Benny the Beluga) residing in a stretch of the river within close proximity to the survey area. A conservative approach was developed in liaison with Natural England and the JNCC and surveys were conducted successfully without disturbance or injury to any marine mammals.