Black cottonwood has previously been featured on BPotD here: Populus trichocarpa. Two resources to add to those listed there: the Silvics of North America treatment of Populus trichocarpa and GRIN’s Populus balsamifera subsp. trichocarpa (a synonym; the previous BPotD touches on the naming issue).
This photograph was taken on the shores of Medicine Lake in Canada’s Jasper National Park. “Medicine Lake” should actually be in quotes — it’s not a true lake, as it only exists for part of the year. The in-flowing Maligne River backs up in this area for several months of the year due to the volume of glacial meltwater, forming the lake-like body. The water slowly drains via a series of sinkholes, travels through a cave system and then emerges 16km / 10miles downstream in Maligne Canyon. You can estimate the summer high-water mark from the band of vegetation-free shoreline.
Entomology / photography resource link: Via the Zooillogix weblog, mantis photographs by photographer Igor Siwanowicz. If you want to see more of Siwanowicz’s work (and trust me, you want to), visit his photo.net gallery: Igor Siwanowicz.