var target: Transform;
    var mesh: NavMesh;
    private var agent: NavMeshAgent;
    private var waterLayer: int;
    function Start () {
        agent = GetComponent.<NavMeshAgent>();
        waterLayer = mesh.GetNavMeshLayerFromName("Water");
        agent.SetDestination(target.position);
    }
    function Update() {
        var hit: NavMeshHit;
        
        // Check all layers one unit ahead.
        if (!agent.SamplePathPosition(-1, 1.0, hit)) {
            if (hit.mask & waterLayer) {
                // Water detected along the path...
            }
        }
    }

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Transform target;
    public NavMesh mesh;
    private NavMeshAgent agent;
    private int waterLayer;
    void Start() {
        agent = GetComponent<NavMeshAgent>();
        waterLayer = mesh.GetNavMeshLayerFromName("Water");
        agent.SetDestination(target.position);
    }
    void Update() {
        NavMeshHit hit;
        if (!agent.SamplePathPosition(-1, 1.0F, out hit))
            if (hit.mask & waterLayer) {
            }
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public target as Transform

    public mesh as NavMesh

    private agent as NavMeshAgent

    private waterLayer as int

    def Start():
        agent = GetComponent[of NavMeshAgent]()
        waterLayer = mesh.GetNavMeshLayerFromName('Water')
        agent.SetDestination(target.position)

    def Update():
        hit as NavMeshHit
        if not agent.SamplePathPosition(-1, 1.0F, hit):
            if hit.mask & waterLayer:
                pass