  In this paper, we show that every quasiorder $R$ induces a Nelson algebra
$\mathbb{RS}$ such that the underlying rough set lattice $RS$ is algebraic. We
note that $\mathbb{RS}$ is a three-valued {\L}ukasiewicz algebra if and only if
$R$ is an equivalence. Our main result says that if $\mathbb{A}$ is a Nelson
algebra defined on an algebraic lattice, then there exists a set $U$ and a
quasiorder $R$ on $U$ such that $\mathbb{A} \cong \mathbb{RS}$.
