Flame, I second the note from Essup. There are some great threads in the archives. In my case, I've created some piles along the shoreline with a mixture of rip rap, dirt and brush in my two-acre pond. I used rip rap (cinder blocks would be a cheaper option) and dirt to help hold the brush in place. I also have a shallow area, a sort of shelf, where I can place brush until I can establish some aquatic plants. Like you, I have an abundance of pine trees as well as cedar trees and I plan to add them over time for cover as I clear my fence rows. So, I've researched this a bit and there's not a wealth of information out there specific to conifers. But, here's what I've found...
A general rule of thumb is that 20% of the pond should have cover. For a 2-acre pond, that's 0.4 acre of cover. It seems to me that a mix of pine & cedar brush with aquatic vegetation would be a good goal. Regardless, if you have more than 20% cover, your predator fish may not be able to keep the population of your forage fish in check and the forage fish will soon overtake your pond.
Given that guideline, brush has a number of benefits in a pond. The bacteria that break down brush generate beneficial enzymes which reduce phosphorous and nutrient levels and, in turn, the amount of 'muck' and (smelly) algae in the pond. Bacteria break down the sap (terpenes) of conifers such as pines and cedars much faster than the cellulose material. The decomposed sap produces isoprenoids and essential oils which are beneficial to micro-organisms and plants. I can't find any mention of toxic by-products for fish. However, an excess of brush (and by inference, bacteria) will lower the DO which is essential to maintaining healthy fish. On the flip side, aquatic plants generate DO and, of course, you can provide artificial aeration to increase the DO level as well.
So, if you have a lot of aquatic vegetation and/or an aeration system, then (in theory) you could use a larger percentage of brush over other types of cover. Regardless, I wouldn't add more than 20% of total cover to the pond.
