What can an umpire do when a crew interferes with another crew?

What counts: a crew interferes if its oars, sculls or boat encroach into the opponent's lane and cause a disadvantage by contact, wash or other distraction. The Umpire alone decides whether a crew is in its own lane or interfering (Rule 80).

Steps and signals (By-Law to Rule 80):

• Alert: if a crew is about to interfere by wash or leaving its lane, the Umpire shows the white flag, calls the crew by name and lowers the flag to the side it must steer towards. Otherwise the Umpire may not give steering indications unless there is an obstruction in the lane.
• Stop: to protect competitors and equipment, the Umpire raises the white flag vertically, names the crew and says "Stop". The crew may row on to finish only if the Umpire permits.
• Remedy first: if a crew is disadvantaged, the priority is to restore its chances; a sanction is secondary. The Umpire may stop the race, sanction and order a re-row, or let the race continue and announce the decision afterwards. The Umpire may not sanction the crew at fault while the affected crew's chances are not restored.

Powers:

• A crew that causes interference that, in the Umpire's opinion, affected another crew's finishing position may be excluded.
• After a collision of boats, oars or sculls, the Umpire may exclude the crew causing it even without prior warning.
• Sanctions may be imposed without prior warning (Rule 98.2).
• The Umpire may decline to order a re-row if the impediment did not affect the result or its effect was not significant (Rule 98.4).
• The Umpire may allow the race to continue and exclude crews after it has finished.
• In no case may the Umpire alter a placing.