Irrigation canals have a series structure which is generally used to design multivariable controllers based on the aggregation of decentralized monovariable controllers. The paper first reviews classical upstream and downstream control strategies, in terms of stability, performance and robustness. Second, a new structured mixed control scheme is proposed, leading to a fully multivariable controller, with guaranteed stability. This controller enables to mix the advantages of both classical control politics: it recovers the local upstream control performance with respect to unpredicted withdrawals, while at the same time ensuring that the water resource is efficiently managed, as in the downstream control case. It can be implemented in a semi-decentralized way, so that each localized controller only communicates with its closest neighbors. It provides an interesting framework for general design of multivariable controllers for irrigation canals