Many central questions in river ecology and management rely on understanding the distributions of aquatic plants and their habitats. However, it remains difficult to map submerged aquatic vegetation and relevant habitat characteristics in rivers at scales beyond the scope of field surveys. We focus here on rocky shoals, which are the principal habitat of the riverine macrophyte Podostemum ceratophyllum Michx. This species is considered an indicator of the overall ecological health of the rivers it inhabits, including the well-being of several fish and invertebrate species of conservation concern. Here, we provide a map of known and likely rocky shoal habitats in three rivers in Georgia, USA, produced by a manual survey in Google Earth Pro using simple, repeatable criteria. We intend for this map to aid ongoing and future efforts to locate rocky shoals in these rivers, model the distribution and growth of associated species, and identify prospective shoals in other systems.

To establish an initial map of habitats potentially suitable for Podostemum, we used Google Earth Pro to search for rocky shoals along the lengths of the Middle Oconee, Conasauga, and Etowah Rivers in northern Georgia. For this purpose, we defined shoals as river reaches ≥10 m long in which rocky substrate (submerged or emergent bedrock, boulder, or cobble) was visible and turbulence was evident on the water surface at multiple time points, indicating consistently rapid water flow. Shoals separated from each other by ≥10 m were considered distinct; shoals separated by <10 m were combined. Shoal-like habitats apparently associated with historical indigenous fishing weirs (Cook, 2013) were counted as shoals. Non-shoal reaches were marked by sandy substrates and a consistent lack of turbulence on the water surface. 

We used several sets of field observations to support this search, including GPS records of shoals sampled in previous and ongoing experiments (Argentina et al., 2010a; Argentina et al., 2010b; Baker 2012; Freeman et al., 2017; Marcinek 2002 unpublished) and river guides for recreational paddlers (Cook, 2013; Cook, 2019). We also included river start and end points and flowlines (USGS NHD, 2023).

This technique is sensitive to limitations in available imagery and our interpretations thereof. We strove to identify every location that was likely to be a rocky shoal, but factors such as narrow channel width, high tree cover, and high water level may have masked some shoals from detection. Similarly, classification of a shoal by the above criteria does not guarantee that a given habitat is actually a shoal, nor that it contains Podostemum. 

The .kmz data file can be opened in several spatial analysis programs including Google Earth. For a detailed guide to this dataset, please see the .pdf metadata file.