According to Official Guinness Records,
The longest distance marathon pool rescue was 30,000 m (98,425 ft) by members of the Frinton and Walton Swimming Pool Lifeguard Team (UK) at Frinton and Walton Swimming Pool in Walton on the Naze, UK, on 8 July 2011.
The event consisted of 23 team members, each towing a manikin heavier than 40 lb (18.14 kg) in continuous legs along a 25-m pool. Each member was required to swim at least 50 m before passing on to the next team member. The event lasted 15 hr 30 min 33 sec.
For a complete list of 2011 records, please visit 2011 Guinness Records in United Kingdom.