Types of Christmas trees for fish and other aquatic life.

Happy 2022! I wanna find out how can we put our old Christmas trees into our ponds, lakes, streams and rivers to help fish and other aquatic critters for shelter for breeding and protection from predators. I've never done it before in my backyard when I had my pond. I wanna find out which types of Christmas trees are safe for underwater creatures. Please let me know in this forum if you all have anything to add. Out!

I love the idea, but I would have some serious trepidation about it. Alas, most Christmas trees are sprayed with various herbicides and pesticides, the main eight being chlorothalonil, atrazine, simazine, glyphosate, hexazinone, carbaryl, chlorpyrifos and dimethoate. Several of these are known to pose extreme harm to aquatic organisms. Of course, we really have no way to know how much residue from these chemicals remains on the trees. It is known that many of these chemicals cause harm in very small doses. To me, it doesn't feel worth the risk. So I personally choose to err on the side of caution and avoid these trees. Even though it pains me greatly to see all the potential habitat for wildlife laying on the curb, bound for the dump. If it weren't for the chemicals, I would have a grove of old Christmas trees set up in my yard.  
Obviously, if you could find trees that were organic or you could be certain had not been sprayed, I would say go for it. They seem to be somewhat tough to find though.

Here's some more detailed info on the chemicals that are used and how common their use is:https://christmastrees.ces.ncsu.edu/faq-pesticides-used-in-christmas-trees/
And this one has a bit more about the effects of those chemicals on life: https://medium.com/center-for-biological-diversity/are-christmas-trees-sprayed-with-pesticides-67d832f8556d

We switched long ago to an artificial tree, so we no longer participate in the whole "tree farm industry" ... while I wasn't aware of all the chemicals that might be present, I was very aware of the house fire danger of "fresh xmas trees".

Our next iteration, living on pine forested acreage, will be to explore a truly "live" tree ... one with a good shape & needles suitable for tree ornaments, but that is planted and continually growing. We only have black pine & some pondy's, but are experimenting now with various other pines brought in ... if we can keep them alive, one might rise to the top as the best candidate for this xmas tree proposal.

WRT the use of trees in pond water ... if you had live ones (no chemicals in sight) that you grow/cut, then perhaps when all their needles have dropped, the trunk/branches would make a safe habitat. Nothing (very little) grows where the needles drop on our acreage, so not sure you want to put all that needle load into the water, but maybe trunks w/ branches attached would work. Or some other kind of tree ...

Or, drop a battleship in there ... these are scuttled in the ocean all the time, and form great reefs for the ocean flora/fauna. Or your homestead equivalent of a battleship ... bbq pit?

We don't have coral in our ponds, but perhaps some kind of lattice material that algae can grow on ...

Did your fish and stuff benefited from your efforts in your pond? How do artificial trees work?

Didn't do branches/trunks in our (small) ponds ... didn't want "rotting" material in them; because we have only pines, not sure the trunks or branches don't have the same content as needles.

Still trying to determine what an appropriate "lattice" material would be ... hopefully, something inert that is gathering dust on our homestead.

Many years ago when I lived in Cache Valley, local sportspeople and the Fish and Game had Christmas tree collection drives.  Hundreds of unflocked and untinseled trees were gathered and tied together in dozens of piles on the ice of  local reservoirs that were experiencing low natural fish reproduction because there was not much habitat available for baby fish to hide in. The weighted piles of trees sank when the ice melted and over time the fishing was much improved.  I don't think anybody considered the chemical aspect of the trees at the time and there were ag chemicals going into the lakes from the surrounding farm land anyway.

Which types of fish were there in the Cache? Was the habitat stable long ago when you were there?

They were trying to improve the fishery for Yellow Perch, Bluegill, Crappie, and Largemouth Bass, as well as providing cover for prey species.
As I recall fish surveys in the early 1980s in some of the reservoirs showed a lack of juvenile fish and the Christmas trees were part of the solution. WE moved away in 1988 and I haven't kept track of the fishing since then.
The original habitat probably wasn't all that stable because the water levels fluctuated with the irrigation season.
One of my friends told me that they also tried tire piles in a similar fashion.

Is the Cache still around? Must've taken a long time to clean the mess they left you all.