  This study presents numerical simulations of faecal coliforms dynamics in
Luruaco lake, located in Atl\'antico Department, Colombia. The velocity field
is obtained through a two-dimensional horizontal (2DH) model of Navier-Stokes
equations system. The transport equation of faecal coliforms concentration is
provided from a convective-diffusive-reactive equation. The lake's geometry is
built through cubic spline and multi-block methods. The discretization method
by Finite Differences and the First Order Upwind (FOU) are applied to the 2DH
model. The Mark and Cell (MAC) method is used to determine numerically the
velocity field of water flow. Numerical simulations are carried out for a
72-hour period in order to understand the influence of faecal coliforms
injections from each tributary. From the qualitative and quantitative analysis
of the factors that influence faecal coliforms dynamics, proposals are
presented, which aim to reduce contamination in some regions of Lake Luruaco.
The numerical simulations show that the best option to improve water quality in
the lake is the implementation of two actions, the diversion of the Lim\'on
stream to the Negro stream and the installation of a sewage treatment plant at
the mouth of the Negro stream. Other less expensive proposals are also
presented.
