The San Jacinto River is expected to crest near 72 feet Wednesday afternoon amid the rising waters due to rain upstream from storms earlier this week.
And the threat may not be over yet.
The ABC13 Weather Team declared the rest of the day Wednesday and into Thursday morning a Weather Alert Day as there's a threat for more heavy rainfall. A storm Thursday morning could bring gusty, winds, hail and a brief tornado.
Overnight, Harris County Precinct 3 and the Harris County Sheriff's Office responded to high water rescues in the Idle Wild area of New Caney, the agencies said.
"The high water vehicles have been running rescues all night. Oddly enough, we've rescued more animals than people. At this point, I believe about a dozen folks have been pulled out and rescued, per their requests. And almost three dozen animals, dogs and cats specifically," Sgt. Jeff Mabery, with the Harris County Sheriff's Office Patrol Dist. 2, said.
Precinct 3 said at about 3:45 a.m. that in the New Caney and Huffman areas, Spaulding Road, Casey Road from FM 1485 to the dead end and the Idle Wild neighborhood are all experiencing high water from the river.
FM 1485 is expected to reman impassable for a few days.
WATCH: Flood rescue crews jump into action as leaders say threat isn't over
While evacuations are still voluntary, emergency officials in Harris and Montgomery counties alerted people living close by the San Jacinto River's East Fork of the threatening water levels.
On Tuesday, the National Weather Service issued a Flood Warning for the east fork near New Caney, impacting Liberty, Harris, and Montgomery counties.
In addition, emergency officials identified five neighborhoods that are expected to be impacted: Idle Glen Subdivision, Northwood Country Estates, River Terrace, Cypress Point, and the Kingwood area.
Meanwhile, Harris County offered the Leon Grayson/Baldree Community Center as a place of shelter. It's at 13828 Corpus Christi St. in Houston.
According to the county, if residents are already seeing high water near their home, they're being urged not try to drive themselves to the shelter. Instead, officials directed people to call 911, and first responders will bring them to a safe location.
The shelter will have cots, blankets, food and water available, the county added. This shelter will also accept pets if they are crated.
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WATCH: ABC13 livestream coverage of Harris County leaders preparing for flood threat