diff --git a/src/pathfinder/water_regions.h b/src/pathfinder/water_regions.h
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+++ b/src/pathfinder/water_regions.h
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+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+ /** @file water_regions.h Handles dividing the water in the map into regions to assist pathfinding. */
+
+#ifndef WATER_REGIONS_H
+#define WATER_REGIONS_H
+
+#include "tile_type.h"
+#include "map_func.h"
+
+using TWaterRegionPatchLabel = uint8_t;
+using TWaterRegionIndex = uint;
+
+constexpr int WATER_REGION_EDGE_LENGTH = 16;
+constexpr int WATER_REGION_NUMBER_OF_TILES = WATER_REGION_EDGE_LENGTH * WATER_REGION_EDGE_LENGTH;
+
+/**
+ * Describes a single interconnected patch of water within a particular water region.
+ */
+struct WaterRegionPatchDesc
+{
+	int x; ///< The X coordinate of the water region, i.e. X=2 is the 3rd water region along the X-axis
+	int y; ///< The Y coordinate of the water region, i.e. Y=2 is the 3rd water region along the Y-axis
+	TWaterRegionPatchLabel label; ///< Unique label identifying the patch within the region
+
+	bool operator==(const WaterRegionPatchDesc &other) const { return x == other.x && y == other.y && label == other.label; }
+	bool operator!=(const WaterRegionPatchDesc &other) const { return !(*this == other); }
+};
+
+
+/**
+ * Describes a single square water region.
+ */
+struct WaterRegionDesc
+{
+	int x; ///< The X coordinate of the water region, i.e. X=2 is the 3rd water region along the X-axis
+	int y; ///< The Y coordinate of the water region, i.e. Y=2 is the 3rd water region along the Y-axis
+
+	WaterRegionDesc(const int x, const int y) : x(x), y(y) {}
+	WaterRegionDesc(const WaterRegionPatchDesc &water_region_patch) : x(water_region_patch.x), y(water_region_patch.y) {}
+
+	bool operator==(const WaterRegionDesc &other) const { return x == other.x && y == other.y; }
+	bool operator!=(const WaterRegionDesc &other) const { return !(*this == other); }
+};
+
+TWaterRegionIndex GetWaterRegionIndex(const WaterRegionDesc &water_region);
+
+TileIndex GetWaterRegionCenterTile(const WaterRegionDesc &water_region);
+
+WaterRegionDesc GetWaterRegionInfo(TileIndex tile);
+WaterRegionPatchDesc GetWaterRegionPatchInfo(TileIndex tile);
+
+void InvalidateWaterRegion(TileIndex tile);
+
+using TVisitWaterRegionPatchCallBack = std::function<void(const WaterRegionPatchDesc &)>;
+void VisitWaterRegionPatchNeighbors(const WaterRegionPatchDesc &water_region_patch, TVisitWaterRegionPatchCallBack &callback);
+
+void InitializeWaterRegions();
+
+struct WaterRegionSaveLoadInfo
+{
+	bool initialized;
+};
+
+std::vector<WaterRegionSaveLoadInfo> GetWaterRegionSaveLoadInfo();
+void LoadWaterRegions(const std::vector<WaterRegionSaveLoadInfo> &save_load_info);
+
+#endif /* WATER_REGIONS_H */