Presumably they haven't checked all of the river yet 

The husband must have a cast iron alibi 

He doesn’t need an alibi. 

everybody needs an alibi m99

he probably has one anyway, it was a workday morning

I expect he has an alibi or we would have heard more about it by now. Tbf what Martian said. It's possible she really did fall and fell unconscious in some freak accident, though it seems extraordinary. 

A pack of Otters can strip a 200lb carcass in little over 20 minutes

probably

I’m fact a pack of starving otters might just go for a lone human. The river folk say strange things happen down in dingly dell. 
 

It’s near Blackpool so you know there are probably a load of odd people there too.

Case closed! It was the starving otters 

Because rivers move quickly and take anything that isn't nailed down with them.

And bodies sink / float depending on what stage of decomposition they are at, and what the gases inside them are doing.

There are various sections of rivers where loose items will 'collect' and the Environment Agency will be all over this to help direct searches.  

"fell"

Combined with the fact that the divers can’t see and are having to search a whole river by touch.

If the tide was out how deep would that relatively modest stream be?

It was the butler wot did it, I suspect.

On the basis it’s over 15 feet then even with a big tide it will still be over six feet.

Why can’t the otters see?

wang notm7

with the lead piping 

"The husband must have a cast iron alibi"

"He doesn't need an alibi"

Correct, in the circs he would perhaps just need lots of cast iron!

The search has now moved to the sea....

Which is about as surprising as finding out Boris has had another child.

Only took 12 days or so.