I remember very little about this book so here goes:

1) The characters were teenagers
2) They created a Loch Ness monster to put in the local lake or
waterway to scare everyone
3) There was a house that was haunted and they went to prove it a fake
or they set up the house to be haunted to scare others

This was one book with multiple adventures where the kids utilized
their mechanical and scientific knowledge and it usually got them in
trouble.

Hi Mjmalj!

I believe the book you have in mind is The Mad Scientists' Club by
Bertrand R. Brinley and Charles Geer.

Here are two customer reviews from Amazon:

?I remember reading The Mad Scientists' Club for the first time when I
was only about eight years old. I must have read and re-read that book
from cover to cover over a dozen times since. It is a collection of
stories about the escapades of six boys in the town of Mammoth Falls
who use their wits and scientific knowledge to get in (and out) of all
kinds of fun mischief, including "haunting" a house, creating a lake
monster, and entering a hot air balloon race. Essentially, these six
young men dive head-first into all the kinds of adventures that I
longed to have as a young man.?

(..)

?What's good about the Mad Scientists' Club book is that there are a
bunch of stories in one book, and some are really funny, like the time
they built a Loch Ness Monster and put it in Strawberry Lake. I think
the funniest story in the book is The Unidentified Flying Man of
Mammoth Falls.?

Buy a new copy  of this book at  Amazon:
http://www.amazon.com/exec/obidos/tg/detail/-/1930900104/103-9350218-8696610?v=glance&st=*

Or you can purchase a used copy here:
http://www.amazon.com/gp/product/offer-listing/1930900104/ref=dp_bb_a//103-9350218-8696610?condition=all


Search criteria:
Book fiction youth scientific adventures Loch Ness

I hope this helps!

Best regards,
Bobbie7

That's the one.  Thanks for the help!

Thank you for the five stars and tip!
--Bobbie7