Officers from the British Transport Police said following an investigation of the work at the River Severn viaduct in Shrewsbury, no evidence had come to light of anything "untoward" and the case had now been closed.
The police were called in to investigate after concerns were raised with Shropshire Council by a member of the public who found three dead bats under the bridge last Wednesday.
Fears were raised that a number of bat colonies could have been disturbed, which is a criminal offence.
But following investigations between the police, Network Rail and a senior conservation officer, all parties said they were "satisfied" there was no intent to disturb any bats.
Huw Waghorn, a spokesman for the British Transport Police, said: "BTP officers looked into the matter and have liaised with Network Rail and Peter Charleston, a senior investigator at the Bat Conservation Trust, who is satisfied there was no intent to disturb any bats and there does not appear to be anything untoward.
"There are no criminal offences associated with this incident; therefore this is not a police matter."
Contractors for Network Rail have been working for several months on the viaduct, with work including grit-blasting, repainting and timber repairs.
Work on the bridge restarted this week after a scheduled two-day break on Thursday and Friday just after the discovery of dead bats was made.