Under which river was the world's first underwater tunnel built?

Always scary when traveling in a tunnel underwater be it in a train or vehicle

askim, And there's 2 Mersey Tunnels from the Wirral to Liverpool.

When I saw the question I thought Brunel. I only know Izambard, London sewerage, bridges and train lines. I will look into the other Brunel.

Janny Girl, Newcastle Upon Tyne ,England, we have the Tyne Tunnel

Quite awesome to say the least takes an engineering marvel to accomplish this.