As the episode is titled In Too Deep. It very much suggests that Joanna Marshall might find herself in the deep end.
She confides in her husband Pat and shows her some evidence on the phone. He wipes it telling her that it is for her own future given what she has done. It might be for his own benefit as well.
Molly Marshall finds out about political corruption regarding ambitious council leader Sarah Mackie. She has close links with property developer Jack Radcliffe. Mackie has done some favours for him. Jack has been discharging water into the river that may have caused the flooding.
Sarah's husband Sergeant Phil Mackie suspects his wife is having an affair. Maybe he is also into the corruption.
It looks like Jack Radcliffe's land deal is where the characters criss cross each other regarding the dead body.
It just does not work for me so far as a political or an environmental thriller.
The series is all over the place. You had a flood, after the flood. Some sunny weather where Joanna and Molly talk to each other on the outside pavement of the cafe. Then prospect of more bad weather to arrive.
I suspect if you plan to denounce the council leader as corrupt. Then don't ride home on your bike in the pouring rain.