Rivas has arrived as the MLS expansion club's first Designated Player.
Marsch told TSN 990: "When I first spoke to the Impact back in April part of the discussion of the job and moving forward with the team, also involved certain players that were on their radar. When they spoke about Nelson I was aware of him from just following world football and knew about him.
"I think first of all they are used to the physicality of MLS because it is something that is a big part of the league in Colombia. Then I think there is a grittiness, a toughness to growing up in Colombia and trying to be successful. Then getting a chance to get out of Colombia and find a new life for yourself that now the mentality of the players that come to MLS is strong."