[6][7] At the 2008 Summer Olympics in Beijing, Koll set a new Austrian mark in the 200 m freestyle and recorded the sixteenth fastest time of 1:47.81 on the second night of preliminaries to secure the final spot in the semifinals.

[8][9] The following morning, Koll failed to qualify for the final, as he finished his semifinal run with a fourth-slowest time of 1:47.87, just 0.06 of a second off his record from the preliminaries.

[10] Two days later, Koll swam the start-off leg of the men's 4×200 m freestyle relay, recording his individual-split time of 1:47.72.

Koll and his teammates David Brandl, Markus Rogan, and Florian Janistyn finished the second heat in fifth place and ninth overall, for another national record-breaking time of 7:11.45.

The following year, he posted his fifth-career Austrian record time of 1:43.90 by finishing eighth in the preliminary heats of the men's 200 m freestyle at the European Short Course Swimming Championships in Istanbul, Turkey.