More than 1,000 boats are sailing down the Thames in a flotilla tribute to Queen Elizabeth II's 60 years on the throne.
Hundreds of people ignored the persistent rain and camped out overnight to secure prime riverside spots. Crowds swelled into the thousands on June 3 along the 11 kilometer route.
The Thames barrier is being lowered to slow the river's flow.
The nautical parade promises to be the most spectacular in London for some 350 years.
Among the flotilla vessels will more than three dozen "Dunkirk little ships," private boats that rescued thousands of British soldiers from the beaches of France after the German invasion in 1940 -- a defeat that became a major victory for wartime morale.
The four-day Diamond Jubilee celebrations also included thousands of street parties across the country on June 3.
Prince Charles and his wife, Camilla, the duchess of Cornwall, joined hundreds of people for a damp al fresco lunch on Piccadilly, one of London's main shopping streets.
The celebrations also include thousands of street parties and a pop concert on June 4 in front of Buckingham Palace featuring Elton John and Paul McCartney.
60 Years On British Throne For Queen Elizabeth II
1/22Queen Elizabeth II celebrates 60 years as Britain's reigning monarch.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
2/22Queen Elizabeth II is Britain's longest-serving monarch since Queen Victoria, who reigned from 1837 to 1901. This engraving shows Victoria's wedding to Prince Albert in 1840.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
3/22Members of the British royal family pose around Princess Elizabeth and Philip, Duke of Edinburgh, in the Throne Room at Buckingham Palace on their wedding day, November 20, 1947.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
4/22Elizabeth receives the Sword of State from the Archbishop of Canterbury prior to her coronation ceremony in Westminster Abbey on June 2, 1953.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
5/22Queen Elizabeth II poses on her coronation day, June 2, 1953, nearly 1 1/2 years after she became queen regnant upon the death of her father, George VI, on February 6, 1952. Hers was the first coronation to be televised.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
6/22The queen, Prince Philip, and three of their children (Anne, Andrew, and Charles (left-to-right; their fourth child, Prince Edward, was born four years later) at Balmoral Castle in 1960.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
7/22The queen with two of her sons, Princes Andrew (left) and Edward, read a book at Buckingham Palace during the recording of the queen's Christmas message to the Commonwealth in 1971.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
8/22The queen poses with Prince Charles and his fiancee, Lady Diana, at Buckingham Palace in March 1981. The heir apparent's adultery scandal and divorce in 1996 sent shock waves throughout the royal establishment and British society.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
9/22The queen and Charles watch horseraces at Epsom following what she famously described as an "annus horribilis," 1992, which saw her two oldest sons separate from their wives, daughter Anne divorce, and a fire destroy part of Windsor Castle.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
10/22The queen (left) and former British Prime Minister Margaret Thatcher arrive for a dinner to celebrate the latter's 70th birthday in London in 1995.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
11/22Queen Elizabeth II is greeted by well-wishers on a visit to the newly reconstructed Queen Elizabeth Hospital in London in 2001.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
12/22Queen Elizabeth II and Prince Philip attend a service to celebrate their diamond wedding anniversary, in Westminster Abbey in London, in November 2007.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
13/22Queen Elizabeth II unveils a portrait bust by sculptor Oscar Nemon at the House of Lords in London in October 2009.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
14/22The queen's eldest son and heir apparent, Prince Charles, kisses his mother's hand at a Royal Horticultural Society event in 2009.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
15/22Queen Elizabeth II places a wreath at Ground Zero in New York, the scene of two of the Al-Qaeda attacks that killed thousands of Americans and other nationals on September 11, 2001.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
16/22Mounted police officers patrol outside Buckingham Palace in London.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
17/22The queen leaves Buckingham Palace in a horse-drawn carriage to attend the State Opening of Parliament in May 2010.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
18/22Queen Elizabeth II and her husband, Prince Philip, walk through the Royal Gallery in the Palace of Westminster during the State Opening of Parliament in London in May 2010.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
19/22Elizabeth and Philip (front row, center) pose for an official photograph with the Grenadier Guards after presenting the regiment with their new colors in 2010.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
20/22The queen meets with the head of the Roman Catholic Church, Pope Benedict XVI, in September 2010.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
21/22The queen arrives at the Irish president's residence during her historic visit in May 2011, the first by a British head of state to the Republic of Ireland, which gained independence from the United Kingdom in 1922.
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
22/22Queen Elizabeth II receives flowers after the Sunday Service at West Newton Church in West Newton on February 5, 2012, the eve of her Diamond Jubilee (60th anniversary).
Eighty-six-year-old Queen Elizabeth II was marking her Diamond Jubilee on June 4. Elizabeth, who took up the throne after her father, George VI, died in February 1952, is Britain's longest-serving monarch after Queen Victoria, who reigned for more than 63 years.
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The celebration kicked off on June 2 with a royal day at the races, as the queen watched a horse with the courtly name of Camelot win the Epsom Derby.
The 86-year-old monarch and her husband, Prince Philip, visited Epsom racecourse south of the capital for the derby, one of the year's biggest horse-racing events.
The queen is a racing fan and horse breeder who has attended the derby for decades and reads the "Racing Post" each day over breakfast although, unlike many of her subjects, she does not gamble.
Jubilee events end on June 5 with a religious service at St. Paul's Cathedral, a carriage procession through the streets of London, and the queen's appearance with her children, grandchildren, and great-grandchildren on the palace balcony.
The queen took the throne in 1952 on the death of her father, King George VI, and most Britons have known no other monarch.
But not everyone in Britain is celebrating.
The antimonarchist group Republic held a riverbank protest June 3 to oppose the wave of jubilee-mania.
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