The government began releasing water from Krishna Raja Sagar and Kabini dams early yesterday to ensure flow of 9,000 cusecs of water to the neighbouring state.
Police said about 100 people were taken into custody when they squatted on the tracks and detained the Mysore-Shiradi express at Gejjalagere village.
Vehicular movement on the Bangalore-Mysore road continued to remain disrupted for the third consecutive day, they said.
In Mysore, activists of Karnataka Rakshana Vedike staged a dharna in front of the Deputy Commissioner's office.
Chief minister Jagadish Shettar had told reporters on Sunday it was "inevitable" for government to release water to comply with the Apex Court order, but that the state was committed to protect the interests of farmers.
He had also said the state would file a petition before the Supreme Court, seeking a review of its order asking the state to honour the Cauvery River Authority directive to release 9,000 cusecs to Tamil Nadu till Oct 15.
Karnataka has already urged Prime Minister Manmohan Singh, also the CRA chairman, to review its Sept 19 order and keep it in abeyance till the decision was reviewed.