This is The Guardian.

Welcome to The Guardian long read, showcasing the best long-form journalism covering culture, politics and new thinking.

For the text version of this and all our long reads, go to the guardian.com forward slash long read.

I couldn't breathe. The sinister spread of France's killer seaweed by Marta Zaraska,

read by Lucy Bromelo. When her phone rang at around 5pm on the 8th of September 2016,

Rosie Uffre was still at work.

It was one of her daughters, distressed,

calling to tell her that their father, Jean-René,

had not come back from his daily run. Only the family dog had returned, alone and exhausted.

Rosie rushed back home. When she arrived, Rosie noticed that the dog was behaving bizarrely.

She refused to walk, then collapsed under a bush.

Her fur stank of rotten eggs, of overflowing sewers.

Rosie knew where that smell came from.

The mudflats roughly three miles from the family home in Brittany, where seaweed

had been accumulating and putrefying. The soggy, decomposing seaweed stretched for miles along

the shore, sometimes as much as five feet thick, killing other plants and suffocating fish and

small birds.

Rosie and the couple's two children set out on a desperate search along the route of Jean

René's usual run. After about 90 minutes, they found him. His body lay on a crust of

dried seaweed in one of the estuaries that empties into the bay of Saint-Briere in the channel.

A doctor attending the scene suspected a heart attack.

In the shock of those first few days,

...