On the 26th of January 2022 the new Sea Lock IJmuiden in the Netherlands was officially opened. Before the lock was put in use, two in-situ measurement campaigns have been carried out to verify the performance of the lock and after one year of operation a third measurement campaign was performed. The present paper provides an overview of these three monitoring campaigns conducted in the first two years of operation. The measurements verified that the lock performed within predetermined requirements and outcomes of the measurements were used to derive safe procedures for vessel handling during lockage. The findings were in good agreement with expectations from physical scale model research and numerical simulations performed earlier in the design process of the lock. For Sea lock IJmuiden, density currents play a major role in the lock operation. Better understanding of these processes led to a safer lock operation. A fundamental aspect for the success and usefulness of these measurement campaigns was the cooperation between all parties involved in the locking process.