Horrified exclamation after letters from northeast allude to lake with problematic algal bloom (5)

I believe the answer is:

neagh

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'horrified exclamation after letters' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'northeast allude to lake with problematic algal bloom' is the wordplay.
I cannot really see how this works, but
'northeast' could be 'ne' (abbreviation) and 'ne' is located in the answer.
This explanation may well be incorrect...

'from' is the link.

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I've seen this clue in The Irish Times.

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