The third of the five-episode series saw the comedian visit the west of England, drifting along the Rivers Wye and Severn.
'Rivers' picked up an extra 200,000 viewers since its first episode to reach 4.9m viewers and take a 22% share of viewing.
The second of ITV1's three-part crime drama 'Single-Handed', starring Ian McElhinney and Gwen McDonnell, attracted 3.5m and a 17% share. It easily beat its predecessor 'Whatever it Takes' which fizzled out with 2.7m viewers in the same time slot two weeks ago.
Over on BBC Two Louis Theroux's insight into 'The City Addicted to Crystal Meth' drew a respectable crowd of 2.7m, equivalent to a 12% audience share, while 'Big Brother' managed 1.9m viewers at 9pm and 374,000 an hour later on Channel 4+1.
Channel Five drew 1.4m with 'Flight of Fury', the poorly-rated straight-to-DVD Steven Seagal thriller, which aired from 9pm-11.05pm.
On Saturday night, with BBC One stalwart 'Casualty' having finished its run last week, ITV1 profited with 'A Touch Of Frost' gathering 3.5m viewers between 9.20pm and 11.20pm.
The resulting 21.1% share was bigger than BBC One's 16.3% and 3m viewers for Hugh Dennis sitcom 'Outnumbered' at 9.25pm-9.55pm.
'Who Wants To Be A Millionaire?' at 8.20pm-9.20pm also gave ITV1 a bigger share of the audience than BBC One's 'The National Lottery: Guesstimation' at 8.30pm-9.25pm.
The Chris Tarrant quiz scored 3.9m viewers and a 21.6% share to the Lottery game show's 3.6m viewers and 19.9% share.
But BBC One secured the evening's biggest ratings, 4.6m viewers, for obstacle course challenge 'Total Wipeout' at 7.30pm-8.30pm. The Richard Hammond-fronted show was watched by 27.2% of the audience, with ITV1's 'An Audience With Neil Diamond' lagging on 2.9m viewers and a 17.3% share.
Earlier in the evening football made a return after the summer break with 3.2m watching BBC One's live coverage of Championship match West Bromwich Albion vs Newcastle at 5.20pm-7.30pm, giving the channel a 24% share.
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