As the San Antonio River passes under Loop 1604 in south Bexar County, it becomes a different kind of river.

It's no longer a tourist attraction sitting between cement walls. Nor is it the sculpted backdrop of a park.

Here it's as close as it will ever get to being a wild river.

Come January, the San Antonio River Authority is inviting the public to experience the river in its original form by opening two new parks connected by the 13-mile-long Saspamco Paddling Trail.

“People don't know the San Antonio River goes beyond the city,” SARA spokeswoman Laura Waldrum said.

Once beyond the city limits, the river not only is free of the city's regulations that forbid anyone touching it, but it also has cleaned itself enough to meet swimming standards.

With no rapids, the only challenges of the river as it flows at less than 2 mph are the submerged logs.

While natural, the logs are a reminder that the river is not pristine — they collect the floating detritus of humans, mostly thousands of plastic water bottles.

“That's an ongoing problem for any river that is downstream from a major city,” said Steven Raabe, director of technical services at SARA.

But because of the devastating floods of 1946, 1998 and 2002, the floating garbage is the only obvious sign of human impact.

After 1998, the federal government started to buy out those who lived in the river's flood plain, and there are no structures along the river's edge today.

What the floods left are high banks lined with mature cottonwood and willow trees. Turtles, egrets and fish are spotted every few minutes.

But the river is by no means free of human intervention.

Because the river starts in the middle of a metropolis, any rainstorm translates into an instant flood downstream.

A sudden 2-inch rainfall in San Antonio can mean the river rises 30 feet in less than three hours at Loop 1604.

These floods literally carry thousands of tons of sediment.

It is along the Saspamco Paddling Trail that much of this sediment is deposited, creating the 20- to 30-foot-high banks, explained Mike Gonzales, deputy director of technical services at SARA.

He estimates the river's banks were closer to 10 feet high and did not have the near-vertical slope before San Antonio was developed.

But by far the most telling human impact on the river is its daily rise and fall.

The paddling trail is named after the small community of Saspamco, which was named after the now-closed San Antonio Sewer Pipe Manufacturing Co.

The river's flow is a direct result of the sewer that still flows through those clay pipes in San Antonio.

The development of the city all but stopped the springs that fed the San Antonio River. In their place, sewer treatment plants now dictate the fluctuation of the river. Although the water they put out is near drinking water standards, it is by no means as steady as the flow from the river's springs, and it spikes in mid-morning and early evening.

Further, CPS Energy has an intake for the cooling lakes of its power plants right below the city's largest treatment plant.

The utility has the legal right to reduce the river's flow to 10 cubic feet per second to keep the cooling lakes of its power plants full.

The river hit those lows this summer.

SARA recommends a minimal flow of 60 cfs to keep the aquatic species of the river healthy, and 120 cfs to paddle.

But now that the summer heat is gone, along with its high evaporation rate, the river is back to being floatable.

“Right now, I like to call it prime time for paddling,” Gonzales said.