We show that in the continuum limit watersheds dividing drainage basins are Schramm-Loewner Evolution (SLE) curves, being described by one single parameter κ. Several numerical evaluations are applied to ascertain this. All calculations are consistent with SLEκ, with κ = 1.734 ± 0.005, being the only known physical example of an SLE with κ < 2. This lies outside the well-known duality conjecture, bringing up new questions regarding the existence and reversibility of dual models. Furthermore it constitutes a strong indication for conformal invariance in random landscapes and suggests that watersheds likely correspond to a logarithmic Conformal Field Theory (CFT) with central charge c ≈ −7/2.PACS numbers: 89.75. Da, 64.60.al, 91.10.Jf The possibility of statistically describing the properties of random curves with a single parameter fascinates physicists and mathematicians alike. This capability is provided by the theory of Schramm-Loewner Evolution (SLE), where random curves can be generated from a Brownian motion with diffusivity κ [1]. Once κ is identified, several geometrical properties of the curve are known (e.g. fractal dimension, winding angle, and leftpassage probability) [2,3]. Among the examples of such curves, we find self-avoiding walks [4] and the contours of critical clusters in percolation [5], Q-state Potts model [6], and spin glasses [7], as well as in turbulence [8]. Establishing SLE for such systems has provided valuable information on the underlying symmetries and paved the way to some exact results [5,9,10]. In fact, SLE is not a general property of non-self-crossing walks since many curves have been shown not to be SLE as, for example, the interface of solid-on-solid models [11], the domain walls of bimodal spin glasses [12], and the contours of negative-weight percolation [13].Recently, the watershed (WS) of random landscapes [14][15][16], with a fractal dimension d f ≈ 1.22, was shown to be related to a family of curves appearing in different contexts such as, e.g., polymers in strongly disordered media [17], bridge percolation [14], and optimal path cracks [18]. In the present Letter, we show that this universal curve has the properties of SLE, with κ = 1.734 ± 0.005. κ < 2 is a special limit since, up to now, all known examples of SLE found in Nature and statistical physics models have 2 ≤ κ ≤ 8, corresponding to fractal dimensions d f between 1.25 and 2.Scale invariance and, consequently, the appearance of fractal dimensions have always motivated to apply concepts from conformal invariance to shed light on critical systems. Archetypes of self-similarity are the contours of critical clusters in lattice models. Already back in 1923, Loewner proposed an expression for the evolution of an analytic function which conformally maps the region bounded by these curves into a standard domain [19]. Such an evolution, follows the theory, should only depend on a continuous function of a real parameter, known as driving function. Recently, Schramm argued that to guarantee conformal invariance, and...