  In this letter we report {\it in situ} small--angle neutron scattering
results on the high--density (HDA) and low-density amorphous (LDA) ice
structures and on intermediate structures as found during the temperature
induced transformation of HDA into LDA. We show that the small--angle signal is
characterised by two $Q$ regimes featuring different properties ($Q$ is the
modulus of the scattering vector defined as $Q =
4\pi\sin{(\Theta)}/\lambda_{\rm i}$ with $\Theta$ being half the scattering
angle and $\lambda_{\rm i}$ the incident neutron wavelength). The very low--$Q$
regime ($< 5\times 10^{-2}$ \AA $^{-1}$) is dominated by a Porod--limit
scattering. Its intensity reduces in the course of the HDA to LDA
transformation following a kinetics reminiscent of that observed in wide--angle
diffraction experiments. The small--angle neutron scattering formfactor in the
intermediate regime of $5 \times 10^{-2} < Q < 0.5$ \AA$^{-1}$ HDA and LDA
features a rather flat plateau. However, the HDA signal shows an ascending
intensity towards smaller $Q$ marking this amorphous structure as
heterogeneous. When following the HDA to LDA transition the formfactor shows a
pronounced transient excess in intensity marking all intermediate structures as
strongly heterogeneous on a length scale of some nano--meters.
