What are the yellow things?

Took a trip up to Killiecrankie today but had to take a detour via the Sma' Glen because the A9 was closed north of Perth due to a fatal road accident... There doesn't seem to be a week goes by without some sort of accident on that road.

Strapped Kirsten into the Vaude baby carrier and walked down to see the Soldier's Leap and strolled along the river for a bit before turning back and having our picnic outside the visitor centre.

We stopped at Pitlochry on the way back and wandered along to the dam and fish ladder. I was rather intrigued by these bits of blue and yellow tape - there must be a reason for them but what I do not know. If anyone does then please fill me in!