When we think of deadwood we often just think of standing deadwood, dead branches within living crowns, and debris on the woodland floor (be it entire fallen trees or fallen limbs and branches). However, many other forms of deadwood exist, of which submerged deadwood is one (and such deadwood has a significant ecological role). Many species of fish, freshwater invertebrates, and even bryophytes, will benefit from the presence of deadwood.
So next time you see a fallen tree within a pond, lake, stream, or river, consider the implications associated not only with the retention of the deadwood, but also the removal. Can some deadwood remain, if retaining it all is not feasible? Will site visitors (if there are any) be put at risk if deadwood is left? Can niche habitats be encouraged by retaining the deadwood? How will the deadwood impact upon the flow of water? All justified questions (of which there are many more to be asked not listed here), all of which will factor into the final decision.