I would like to do a stream from Reichsbrücke in Vienna, Austria. Reichsbrücke is one of the major bridges crossing the Danube in Vienna. For that purpose I will use two self-built hydrophones that will be hanging from the bridge into the water (2 x 15m cables), connected to a Zoom H5 that will be used as audio device for my smartphone over an OTG adapter.
What you will hopefully hear are the sounds of ships passing by or the motors of the cruise ships laid at anchor on the river shore. Also one might be able to identify the waves a passing-by ship creates.
But even more than that, as I want to record in stereo with two microphones, hanging to the left and right of the center bridge pillar, you may hear the "shadows" the pillar is creating when a ship is passing by to the left or of the pillar.
The physical laws of acoustics under water under water are significantly different from the laws in the atmosphere. E.g. the speed of sound under water is dependent on its frequency. Also physical objects like a bridge pillar have an effect if the source of sound passes by behind it. 
With my little project I would like to give an impression of a world that's normally hidden to our visual and acoustic senses.

Some Details of the construction of my hydrophones
A test setup for an underwater feedback sound system, using my hydrophones and an underwater loudspeaker, including a recording from Donaukanal in Vienna (the speaker under construction can also be seen in the link above)