The others to accomplish the feat are Daryle Ward, Garrett Jones and Pedro Alvarez.
In all, 50 balls have gone into the river, 46 on a bounce, including to two by Bell.
"I honestly never thought about hitting a ball in there on the fly," Bell said. "I didn't know if I was capable of doing that."
The home run was Bell's second-longest of the season at PNC Park. He hit a 474-foot shot over the batter’s eye in center field April 7 against the Reds.
Bell is the only major-league player to have three home runs travel at least 450 feet this season.
Bell has a team-leading nine home runs this season after going deep just 12 times in 148 games last year. He was third in the National League Rookie of the Year voting in 2017, when he belted 26 homers in 159 games.
So what has sparked the power surge? Bell says it is because he has his swing in sync.
“For me, it’s timing with the fastball,” he said. “I continue to get good work in with (hitting coaches Rick) Eckstein and (Jacob) Cruz. I’m focusing on getting my leg kick up in time and just trying to drive the baseball.
"I'm just looking to hit the ball hard every time up and, ideally, I'll barrel a ball up about two out of every five times."
From Clint Hurdle's perspective, he sees a hitter who now has a better plan when he steps into the batter's box. Bell had been a notorious tinkerer, whether it was with his stance, swing path or mindset. However, that all began to change late last season.
"It's all about the consistency of his approach," Hurdle said. "Sometimes we get caught up in chasing results but he's not going down different lanes now. He found some things last September that worked for him and he's staying with them and he's having success because of it."
Bell is hitting .295/.371/.648 with a team-best 27 RBIs in 33 games. Teammate Nick Kingham has been watching the show and is ready to put Bell's name up there with some of the best players in the NL.
"Seriously, you see (Christian) Yelich and (Cody) Bellinger have incredible streaks and hitting the ball like the crazy, but watch out for this guy," said Kingham, who started and had a no-decision. "He's doing some incredible work. He's banging the ball every time he swings, so it’s really fun to watch."