A woman's body has been located in Llano County at a low water crossing.
The body, which hasn't yet been identified, was found in Lake Lyndon B. Johnson, situated where the Llano and Colorado rivers meet.
"We needed the water, we needed the rain".
He called the situation "absolutely hazardous" and said law enforcement would be on patrol.
In response to the severe weather, Gov. Greg Abbott issued a disaster declaration for 18 counties: Bastrop, Burnet, Colorado, Fayette, Hood, Jim Wells, Kerr, Kimble, La Salle, Live Oak, Llano, Mason, McMullen, Nueces, Real, San Patricio, Travis and Williamson.
More rain is forecast for Wednesday and Thursday and flood warnings remain in place for large parts of Texas. In Kingsland, floodwaters swept away a bridge across the Llano River on FM 2900. It is not expected to drop below major flood stage until later on Wednesday.
The Llano River rose to almost 40 feet Tuesday in the city of Llano - about 35 feet higher than it was just 24 hours earlier - after 8 to 10 inches of rain fell in the area over the past two days, the National Weather Service said.
The bridge crumbled as it was overrun by the bloated, roiling Llano River in Kingsland, about 65 miles (105 kilometers) northwest of Austin.
The National Weather Service says "major flooding" is occurring not only along the Llano River, but also the nearby Colorado River and evacuations are underway in the cities of Kingsland and Marble Falls, both northwest of Austin.
Homes also were being evacuated in nearby Granite Shoals and people were sheltering at a middle school.
CBS News came across an emergency team who found and rescued two men trapped in their submerged SUV, nose down in a street that had washed away.
Flooding has closed numerous roads in the area. Forecasters urged those living in vulnerable and low-lying areas along the river to seek higher ground immediately.
"The ongoing multiple days of rain and the extraordinary amount is of course not normal", she said. 'Not for this time of year'.