Natural convection heat transfer from a horizontal ice cylinder immersed in quiescent cold pure water was studied experimentally. The experiment was conducted for the ambient water temperatures ranging from $2.0^{cric}C$ to $10.0^{circ}C$. The flow fields around an ice cylinder and its melting shapes were visualized and local Nusselt numbers obtained. Especially, its attention was focused on the density maximum effects and stagnation point Nusselt number. From the visualized photographs of flow fields, three distinct flow patterns were observed with the ambient water temperature variation. The melting shapes of ice cylinder are various in shape with flow patterns. Steady state upflow was occured at the range of $2.0^{circ}C leq T_{infty} leq 4.6^{circ}C$ and steady state downflow was occured at $T_{infty} geq 6.0^{circ}C$. In the range of $4.7^{circ}C < T_{infty} < 6.0^{circ}C$, three-dimensional unsteady state flow was observed. Especially, the melting shapes of ice cylinder have formed the several spiral flutes for the temperatures ranging from $5.5^{circ}C$ to $5.8^{circ}C$. For upflow regime, the maximum stagnation point Nusselt number exists at $T_{infty} = 2.5^{circ}C$ and as the ambient water temperature increases the Nusselt number decreases. At ambient water temperature of about $5.7^{circ}C$, Nusselt number shows its minimum value.