The presenter - who is mum to baby daughter Betsy with husband Lee Mead, 28 - stumbled across one-and-a-half kilos of the drug behind a cluster of rocks.
'I spotted it from out of the corner of my eye as I went to find a makeshift toilet - a big, clear plastic bag containing loads of white powder,' Denise, 36, tells the Daily Mirror.
'Initially, I couldn't quite believe what I was seeing and wasn't too sure quite what to do with it.
'But I handed it straight over to our security guys who then had to satellite phone through to local police. It was given to them and taken away.
'Apparently it was probably dropped by drug smugglers attempting to cross the border.'
Denise is on a 5-day trek of the Andes for charity Breast Cancer Care.
She's been joined by celeb pals Fearne Cotton and Alexandra Burke and their journey is being filmed for a 2-part ITV2 documentary.
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