A mandatory evacuation was ordered for the low-lying Houston suburb of Dickinson, home to 20,000, and questions swirled in Houston itself about why the mayor did not issue a similar evacuation order.
After days of heavy rain, the Addicks and Barker reservoirs are at record high levels.
More than 17,000 people are seeking refuge in Texas shelters, the American Red Cross said, and the number looks certain to grow.
Meanwhile, an official said that a levee protecting a subdivision of homes in a county south of Houston has been fortified after being breached but warns the threat is far from over.
"This is something we've never seen before", he said.
Harvey made landfall as a category four hurricane before diminishing, but even with the drop in strength, thousands have been displaced by the storm, which made landfall as a category four hurricane. The youngest in the family was six years old.More news: Let's have that debate over paying for the border wall, Mr
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"They need to get out".
Columbia Lakes is located some 50 miles from Houston near the Brazos River.
Rescue boats fill a flooded street at flood victims are evacuated as floodwaters from Harvey rise, August 28, 2017, in Houston.
Rescuers continued plucking people from inundated Houston neighbourhoods.
Brazoria is one of 12 counties Texas Gov. Greg Abbott (R) asked that the Federal Emergency Management Agency (FEMA) add to the presidential disaster declaration.
"This is something we've never faced before", Jeff Lindner of Harris County's flood control district said.