Question: What election was held because of a swimming disappearance?

Context paragraphs:
Australian federal election, 1969: Federal elections were held in Australia on 25 October 1969.  All 125 seats in the House of Representatives were up for election.  The incumbent Liberal Party of Australia led by Prime Minister of Australia John Gorton with coalition partner the Country Party led by John McEwen (who had also served as Prime Minister for three weeks after Harold Holt's disappearance) defeated the Australian Labor Party led by Gough Whitlam.  Even though Labor lost, the election was seen as a good result for the party as it made significant gains against the Coalition.

Higgins by-election, 1968: A by-election was held for the Australian House of Representatives seat of Higgins on 24 February 1968.  It was triggered by the presumed death of then-current Prime Minister and Liberal Party MP Harold Holt.

Harold Holt: Harold Edward Holt, {'1': ", '2': ", '3': ", '4': "} ( ; 5 August 190817 December 1967), was an Australian politician and the 17th Prime Minister of Australia from 1966 to 1967.  He was born in Stanmore, New South Wales and won a scholarship to study law at the University of Melbourne.  Holt went into business as a solicitor, during which time he joined the United Australia Party (UAP).  In 1935, aged just 27, he was elected to parliament for Fawkner.  He held this seat until 1949, when he transferred to Higgins.  Holt spent 32 years in Parliament, including many years as a senior Cabinet Minister, but was Prime Minister for only 22 months before he disappeared in December 1967 while swimming at Cheviot Beach near Portsea, Victoria and was presumed drowned.

Supporting paragraphs: Higgins by-election, 1968 Harold Holt
Answer: A by-election was held for the Australian House of Representatives seat of Higgins on 24 February 1968