The Bills announced the trade of the former South Fort Myers High School star via its official Twitter account.
Watkins has played a total of 37 games since he was drafted in 2014 thanks to constant foot problems. Now L.A. has their No. 1 and 2 receivers from last season, granted Watkins only played eight games past year as he dealt with injuries. He had a career best 1,047 yards and nine touchdowns on 60 receptions in 13 games during the 2015 season.
Some would say the writing was on the wall for Watkins when the Bills declined to exercise the fifth-year option on his contract.
Gaines, 25, had 56 tackles, seven passes defensed and a forced fumble for the Rams in 11 games last season, his second National Football League season.More news: CW to Air Supergirl and Arrow Crossover This Coming Fall
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If Watkins is healthy (which is a big if considering the past two seasons) they have a solid No. 1 receiver to anchor their receiving corps. He's played in 26 games, making 25 starts in three seasons with the franchise. By comparison, the man who will probably replace him in the starting lineup - Matthews, who was the Eagles' second-round pick in 2014 - has missed only two games in his career and has 225 catches for 2,673 yards and 19 TDs.
He'll be an unrestricted free agent next year unless the Rams slap the franchise tag on him.
The two deals see Buffalo add extra second and third-round 2018 draft picks to the additional first-rounder they already held after trading down in this year's draft to allow the Kansas City Chiefs to select Patrick Mahomes. In flashes, he looked explosive, but he just couldn't stay healthy.
The Rams were dead last in yards and scoring last season.