public function getGuidFromRiverId($river_id = 0) {

		$river_id = (int) $river_id;

		$guid = $this->id_cache->get($river_id);
		if ($guid) {
			return $guid;
		}

		$objects = elgg_get_entities_from_metadata([
			'types' => RiverObject::TYPE,
			'subtypes' => [RiverObject::SUBTYPE, 'hjstream'],
			'metadata_name_value_pairs' => [
				'name' => 'river_id',
				'value' => $river_id,
			],
			'limit' => 1,
			'callback' => false,
		]);

		$guid = ($objects) ? $objects[0]->guid : false;

		if ($guid) {
			$this->id_cache->put($river_id, $guid);
			return $guid;
		}

		return false;
	}