“He’ll do to ride the river with” is supposedly a saying from the old west, such as Texas in the 1850s. The saying means that someone (such as a cowboy) can be trusted. A river was a dangerous part of cattle drives.
 
However, the saying appears for the first time in the western stories of novelist William MacLeod Raine (1871-1954). “You’re a good little sport an’ you’ll do to ride the river with” was in Tangled Trails: A Western Detective Story (1921) and “He’ll do to ride the river with” was in Gunsight Pass: How Oil Came to the Cattle Country and Brought a New West (1921). Raine used the expression so often that it became a book title—To Ride the River With (1936).
 
“She’ll Do to Ride the River With” was a 1993 episode of the television drama Walker, Texas Ranger.
 
   
Wikipedia: William MacLeod Raine
William MacLeod Raine (June 22, 1871 - July 25, 1954), was a British-born American novelist who wrote fictional adventure stories about the American Old West.
 
Life
William MacLeod Raine was born in London, the son of William and Jessie Raine. After his mother died, his family migrated from England to Arkansas when MacLeod was ten years old, eventually settling on a cattle ranch near the Texas-Arkansas border.
   
25 January 1922, Sandusky (OH) Star-Journal, “Tangled Trails” by William MacLeod Raine, pg. 6, col. 6:
“You’re a good little sport an’ you’ll do to ride the river with.”
 
Chronicling America
1 March 1922, Seattle (WA) Star, “Gunsight Pass” by William MacLeod Raine, pg. 11, col. 3:
“He’s a good man gone bad.But I’ll say this for Shorty. He’s some man. He’ll do to ride the river with.”
 
12 June 1927, Cleveland (OH) Plain Dealer, “Judge Colt” by William MacLeod Raine, magazine sec., pg. 5, col. 5:
“He’d do to ride the river with. No wonder you’re proud of him.”
 
6 January 1929, Cleveland (OH) Plain Dealer, fiction and feature sec., “Texas Man” by William MacLeod Raine, pg. 7, col. 5:
“That boy will sure do to ride the river with.”
 
2 January 1931, Richardson (TX) Echo, “The FIghting Tenderfoot” by William MacLeod Raine, pg. 5, col. 1:
“Me, I was ready to ride the river with you.”
 
OCLC WorldCat record
To ride the river with
Author: William MacLeod Raine
Publisher: Boston and New York, Houghton Mifflin Co., 1936.
Edition/Format:   Print book : Fiction : English
 
OCLC WorldCat record
One to ride the river with.
Author: Michael Hammonds
Publisher: Garden City, N.Y., Doubleday, 1974.
Edition/Format:   Print book : Fiction : English : [1st ed.]
 
OCLC WorldCat record
Ride the river
Author: Louis L’Amour
Publisher: New York : Bantam Books, 1983.
Series: Sacketts.
Edition/Format:   Print book : Fiction : English
Database: WorldCat
Summary:
No matter that Echo Sackett was young, and a woman, and had never been far from the valley, she was still a Sackett. Sharp and smart and a better hunter than most of the men she knew. Like her bold ancestors, Echo couldn’t ignore a challenge. A sure hand with a horse, a dead shot with a rifle, and fast with her wits, Echo traveled to the mountains of Tennessee, coming up against ruthless killers who’s stop at nothing to cheat her out of her inheritance. There she’d prove once and for all the she could ride the river with the best.
   
IMDb (Internet Movie Database)
Walker, Texas Ranger: Season 2, Episode 7
She’ll Do to Ride the River With (24 Nov. 1993)
TV Episode |  43 min |  Action, Comedy, Crime
When a woman goes against the State Police’s beliefs that her father was a casualty of his own drunk driving, Walker believes her and stumbles across an illegal ring of toxic dumpers.
 
On a Western Trail
Monday, August 22, 2011
HE’LL DO TO RIDE THE RIVER WITH
By Stephen Bly 1944 - 2011
(...)
For many cowboys, his reputation was the only thing of value he could rightly call his own. Lots of terms sprang up that described a man of good character. One of the more meaningful became the phrase “he’ll do to ride the river with,” the highest compliment paid to a cowman.
 
Back in the days of trail drives, cowboys had to swim thousands of heads of cattle across swollen and dangerous rivers. To make it across required riders of exceptional skill, courage, and level-headed thinking. You quickly learned who you could trust to ride those rivers with you.
   
SFGate (San Francisco, CA)
EVERYDAY CHALLENGES.
By Mary Matzek on November 1, 2015 at 8:11 AM
(...)
An old Texas saying was coined around mid-1850s in South Texas. The Nueces Strip was notorious for outlaws, thieves and bushwhackers. The only way a man could be safe was to ride the trail with a loyal partner. From this time and place, the saying “He’ll do to ride the river…” became the highest compliment one cowhand could pay to another.