For years, something has lurked in the rugged gorges of the river country, Australia; terrifying, injuring or killing those who venture too deep, but when one man manages to escape with his life, he sets off a dramatic chain of events that will ultimately reveal the hidden truth.

Many thanks to FFF, dpg and Nir Shelter.
All your comments have been taken on board.
I see what you mean... I think...
I have a difficult aspect of my story in that I am trying to lead the reader into a thinking one thing and then discovering another. So, how to write a logline that does not betray that is proving to be super, super difficult!

sigh!

try, try again :)

This portion of the logline is back story and setup: "...For years, something has lurked in the rugged gorges of the river country, Australia; terrifying, injuring or killing those who venture too deep,?"
The above shouldn't be in your logline. A logline focuses on the present progressive and eludes to the future with the forward motion of a driving goal not the past.

"...a dramatic chain of events?" is a description of all stories ever told and therefore too vague. What is the actual chain of events that take place in your story? It is through their uniqueness that you will be able to structure your plot well and inspire intrigue when telling people about it.

Lastly what is the main character's flaw this will make his journey an interesting one.

Hope this helps.

So the hidden truth is ultimately revealed? So what? What difference does it make in the life of the protagonist (and others)? What are the consequences? What must the protagonist DO about what has been revealed--or else? What's at stake?