THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

Aquatic Invertebrates in Pacific Northwest Freshwater Wetlands
An Identification Guide and Educational Resource

Baetisca lacustris can be collected from sand and detritus only in streams and rivers of the Rockies east. You're not likely to encounter this mayfly through most of the Northwest, but they are distinctive enough that they will be easily identified if you do come across them.

The top of the thorax is broad and covers several abdominal segments. The expanded covering also covers the gills and often has large spines on the sides or top. Like many other mayflies, they have three tails, and and short antennae.