drainage services before flowing then into an urbanized area.

The water quality is worst in the Eslava River at the confluence point, M12, after which either a dilution effect or an artifact of the complex drainage system arises, leading to an apparent improvement in the wastewater quality downstream. Organic matter, such as that found in the discharge, affects the oxygen balance and is usually accompanied by microbiological contamination.

The domestic and agricultural wastes contribute phosphates and ammonia nitrogen. Agriculture also contributes to the dissolved solid levels measured in the river.

The Magdalena Eslava river system could be used more efficiently. The river receives domestic discharge, and a portion of the flow passes through the *Delegación Magdalena Contreras*, where no industry is present.

The construction of at least two wastewater treatment plants isdon't want to spoil it," Dempsie said. "And with these spoilers, it's not just telling a mate a secret. These things will grow exponentially. It only takes them telling two more mates the next day down the pub, and the secret's out.

"With the betting side of it, why would you offer a market on something that quite a large number of people do know the answer to? A considerable number of people!"

Fair point.

However the series finale draws the eight-year saga to a close, Dempsie's convinced that it'll divide opinion. "It's so hard to end anything – to bring anything to a conclusion that you feel is broadly satisfying, and without compromising, and being surprising as well," he explained.

"I've been talking about that a lot with Game of Thrones.