She said:

"i'm curious why the engineering was happening! how do people decide when to let nature take care of itself and when to, for example, remove a dike?"

A: Interesting indeed. The dike was put in years ago...man made. When it was built, the stream became a straight line next to the dike. Streams with bends and with woody debris create fast and slow moving places, trees on the bank keep the water cool and the dirt out of the gravel. Spawning salmon need areas of slow water to rest as they swim upstream, and the baby fish (fry) need pools to hang out in when they come out of the gravel. The smolts swim down the stream to the ocean and are a tasty snack if they have nowhere to hide. Only 2 of 3000 eggs will survive to be spawning adults and return to the same stream, and the salmon are running at record low numbers. Now the engineering is basically to undo the earlier damage; I guess it’s a start at undoing much of the damage that human interference has caused to the Salmon population. In regards to letting nature take care of herself, we do have strict rules about salmon streams. The stream in Twanoh is a salmon stream and there are very strict laws restricting bridge building, dam building, and messing in general. To put in or take out anything from the stream is a big no no. In that regard, they are putting faith in mama to find the right balance.