Cửa biển Lộc An = Loc An sea gate.

Please refer to:

https://www.google.com.vn/#hl=en&sclient=psy-ab&q="Loc An se...

seaport

http://wiki.answers.com/Q/What_is_the_name_of_the_place_wher...
http://en.wiktionary.org/wiki/sea_mouth

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Note added at 1 hr (2013-03-08 04:11:44 GMT)
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ANH THAM KHẢO THÊM ĐOẠN NÀY:

"Loc An resort is located on such a beautiful, unpolluted beach. Loc An SEA MOUTH is situated in region 2, Loc An, Dat Do, Phuoc Buu, Xuyen Moc district, Ba Ria Vung Tau province.

A place where Ray river starts to mix itself into the sea. Coming here, you have a chance to gaze at the natural beauty of sea, forest, white sand hill. Beside this resort lays a cool and pure swimming pool which is suitable for all ages. A variety of bamboo-made long chair is available to meet all requirements of customers who would like to have a rest. It is the fact that Loc An resort has 28 resting rooms included 25 couple rooms and 3 community ones. Rooms listed are designed in a luxurious, cozy way and are equipped with suitable comfort.
Moreover, the majority of items put available in each room is made from bamboo with specifically ethnic style. Also, some other entertaining services offered are: couple bicycle, beach volleyball, lake fishing, billiard, etc." (http://www.vnnavi.com/restaurants/locanvt/en_index.html)

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Note added at 1 day10 hrs (2013-03-09 13:38:18 GMT)
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"Mouth" is a synonym of "estuary". Please refer to http://thesaurus.com/browse/estuary; http://www.learnersdictionary.com/search/mouth (sense 3); http://oald8.oxfordlearnersdictionaries.com/dictionary/mouth (sense 4);

Theo e thấy thì estuary bản thân nó đã có nghĩa là cửa sông rồi
http://tratu.soha.vn/dict/en_vn/Estuary
nên chắc là ko dùng kiểu như sea estuary được.
Còn đây là ngta giải thích về sea mouth: That part of a river, estuary or lagoon which broadens out as it meets the sea
http://en.wiktionary.org/wiki/sea_mouth
Còn sea gate:
Sea gate, a channel or waterway which gives access to the ocean
Vậy sea gate và sea mouth chắc đều dùng đc đó a

Nếu chỉ có một cửa thôi, thì "river mouth" hoặc "mouth of the river" mới đúng. Nếu muốn kèm theo tên của con sông thì thường nói "the mouth of the ..... River v.d. "situated at the mouth of the Loc An River". Trường hợp có nhiều cửa, Sông Cửu Long chẳng hạn, thì có thể nói delta (the Mekong Delta). "Estuary" là một khúc sông, có thể không phải là "cửa". Đối với tôi, "estuary" có chất khoa học, hoặc lối sống cua người nói gần gũi với sông và biển.