The Environment Agency has issued flood warnings for the River Eden and River Caldew near Carlisle.
Warnings are also in place for the River Cocker at both Cockermouth and Southwaite Bridge.
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The first of seven races will begin at 5:45pm, and 76 horses are competing. The UK's top female jockey is amongst the competitors.
Thousands of people are expected to flock to Brampton to catch a glimpse of the colourful breed, which is more common in warmer climates.
More than 120 young athletes are taking part in this year's Borders Sport and Leisure Sports Academy.