The heat prompted some festival goers to jump into the City Hall reflection pond to cool off, converting it into a wading pool.
The event is said to be the largest of its kind in the southwestern U.S.
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The festival has drawn hundreds of thousands of those from the LGBT community, their families and who want to celebrate diversity.
The event began approximately 40 years ago, when singer and conservative activist Anita Bryant came to Houston, to condemn homosexuality.
Gay activist Ray Hill was the outspoken opponent who organized what became the Pride Parade on lower Westheimer.
At the time, police were raiding gay nightclubs in Montrose.
Since then, the festival and parade grew large enough that the event was moved to downtown Houston.
It's traditionally held on the last Saturday in June. Two years ago, attendance was reported at 700,000 people, breaking a record.
A police officer working the festival entrance observed that there was no line to get in, but the streets around City Hall were packed with people of all ages.
A few wore unicorn hats, colored like a rainbow. Others wore rainbow-striped capes and some wore bathing suits.
Some came with their parents.
Two brothers, age 19 and identical twins, wore matching T-shirts and rainbows painted on their faces.
One brother is straight and the other is gay. They appreciate the work done by earlier generations to make their lives easier.
"It would have been tragic (to come out) back then," said Dante Moreno. "I can only imagine what would have happened."
Four protesters with a "Repent or Perish" banner were at the perimeter of the barricades of the festival Saturday.
Whatever was said by protesters was drowned out by the music playing on large speakers.
The parade begins at 8:30 p.m. Saturday, and Houston's own Mayor Sylvester Turner will ride in it.
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