  We calculate the energy of threshold fluctuation $\delta F_{thr}$ which
triggers the transition of superconducting current-carrying bridge to resistive
state. We show that the dependence $\delta F_{thr}(I)\propto
I_{dep}\hbar(1-I/I_{dep})^{5/4}/e$, found by Langer and Ambegaokar for a long
bridge with length $L \gg \xi$, holds far below the critical temperature both
in dirty and clean limits (here $I_{dep}$ is the depairing current of the
bridge and $\xi$ is a coherence length). We also find that even 'weak' local
defect (leading to the small suppression of the critical current of the bridge
$I_c \lesssim I_{dep}$) provides $\delta F_{thr}\propto
I_c\hbar(1-I/I_c)^{3/2}/e$, typical for a short bridge with $L \ll \xi$ or a
Josephson junction.
