Related Clues:

• River with plague at the bottom
• Of the greatest depth
• Flower parasite most difficult to fathom
• River bug, most insidious
• Troublesome creature under river most hard to get at there?
• Furthest down
• River trial is most demanding
• Problem beneath the river, at the very bottom
• Exercise in river and street is hardest to understand
• Most learned to loathe record for the first time
• Girl, a nuisance, being most hard to fathom
• Most profound river bore
• Taking longest for the plumber to get to
• Extremely intense training in river's heading for trouble
• River disease is most serious