Sheep at RSPB Haweswater. Credit: Patrick Neaves
Rail users have been warned to expect delays of up to 30 minutes.
The warning was issued after a number of sheep were found of the lines between Carlisle and Wetheral.
A spokesman for Northern train services said: "Due to sheep on the railway between Carlisle and Wetheral all lines are blocked.
"Train services running through these stations may be delayed by up to 30 minutes.
"Disruption is expected until 12pm today."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here