The Boat Races are always umpired by an "old Blue", with an ex-Oxford umpire alternating year on year with an ex-Cambridge umpire.
The rules of the Races are essentially very simple, the crews must keep to their stations (Middlesex or Surrey) unless they have a lead of "clear water" when if they wish they can use the opposite station. The other rule of note is that both crews must row through the centre arches of Hammersmith and Barnes Bridges.
Both crews try to row the quickest line on the fastest water and they often come perilously close to each other. The umpire trys to ensure neither crew commits a "foul" by warning them to keep to their own racing line. He has the authority to disqualify a crew, though this has only happened once in the modern era; in the Isis/Goldie Race of 1990, when the umpire was John Garrett.
Following the controversial 2001 Boat Race, where Umpire Rupert Obholzer stopped and restarted the Race following a clash of blades, an umpires' panel was established consisting of four umpires from each university, chaired by a senior umpire. The panel shares experiences and pools expertise and has initiated the assistant umpires for the Race.