Henley Royal Regatta on the River Thames by Henley-on-Thames. The Royal Regatta is sometimes referred to as Henley Regatta, its original name pre-dating Royal patronage. Lasts 5 days (Wednesday - Sunday) first weekend in July. Races are head-to-head knock out competitions, raced over a course of 1 mile, 550 yds. The most prestigious event at the regatta is the Grand Challenge Cup for Men's Eights, which has been awarded since the regatta was first staged. It is part of The Season's calendar.