Reposting from what I did with orcs in my homebrew world...
Displaced But Not Forgotten. From their lairs in the Durghessan Highlands and nearby foothills, the orcs look toward the eastern sea with longing. The Highlands, with its human "barbarians" and bitter dwarves to the north, is where the orcs have pitched their sail-tents for several generations, but it is not their home. Long ago, the orcs were driven from the lowlands. Their legends claim that the orcs were born from the womb of the mercurial sea goddess, and ancient orcish prophecies claim the deep sea is their destiny. When their shamans hear the call, the orcs pack up their sail-tents and strap them to the backs of draft horses and water buffalo to make the pilgrimage to the lowlands. There is no predicting this – orcish spirituality is not bound to tradition, but rather is ecstatic and individual in nature – though it never happens in winter when travel is hardest. To humans lacking understanding of the significance of this journey, the orcs appear as raiders descending upon them. This is only half true.
Raiders or Pilgrims? The orcs do take what they need to survive, particularly if it was a hard winter. However, the orcs feel an intense time pressure during this pilgrimage, as the call of the sea echoes in their bones, and the risk of lowlander humans uniting against them grows. They do not wish to tarry in human lands long, and humans who resettle for a night or who can convince or trick the orcs to take a "quicker route" may find their fields and homes untouched by orcish raiders. Additionally, many pregnant mothers undertake this journey, hoping their children will be born in the ocean in a ritual known as the Salten Spear. They do not wish to unnecessarily jeopardize the lives of their mothers and young with needless battle. Providing medical care and midwifery to orcish mothers is a sure way to avoid hostilities. Orcish outriders look proactively for threats to counter, particularly military encampments with horses or other means to rapidly mobilize light cavalry; these are sabotaged in the dead of night, and success on these missions is a bit of a competition to see who can inspire the most shock, awe, and fear – to bring glory to that orc's family in the eyes of the sea goddess. Thus, appearing as no threat or an otherwise unworthy target will avoid drawing the attraction of the orcish outriders.
Culture of Adoption. Like the sea pig (scotoplanes) of our real world which protect baby king crabs from predators, orcs are known for adopting the forgotten, abandoned, and outcast. During these pilgrimages, new blood is brought into the caravan. To the orcish perspective, "sharing the same blood" is a bond formed through overcoming hardships and fighting at one another's side repeatedly. Thus, when visiting the orcs in the Durghessan Highlands or even when encountering them on pilgrimage to the lowlands, travelers may be surprised to see a small percentage of non-orcs living among the orc clans, eating their food, dancing their wild "wind dances", and inter-marrying. Those half-orcs with aquatic elf, water genasi, or triton descent are viewed as especially good omens.
Sea Reavers and Believers. A very small minority of orcs still live on the sea, fashioning shallow draft longships which can go over reef/shoals and journey upriver. Though these ships are ill-suited for long journeys, the creation of one is a long process closely safeguarded by orcish shipwrights. Only a few of these ships remain and the crafting of the ships is a dying art. In the past, these coastal orcs reserved hostilities for those who displeased the sea goddess by failing to give her offerings, conjuring storms without offering the proper rites of respect, or hunting sea life in a wasteful manner. However, in recent years they have increasingly acted as sea reavers, taking "the sea goddess' due" from those who've forgotten her ways. The worst of these coastal orcs demand blood sacrifices. Like their highland kin, the coastal orcs are also known for adopting deserters, orphaned cabin boys/girls, castaways, and captives, integrating them into their clan much like their upland kin. Using animal messengers, the highland shamans and lowland reavers/shipwrights coordinate when a pilgrimage is happening, so that the lowlanders meet their kin at the coast, bearing the statue of the sea goddess on a specially constructed longship. The Salten Spear birthing ceremony and appeasement rites of the sea goddess are closely guarded secrets, and outsiders are absolutely unwelcome (though adopted humans, half-orcs, elves, dwarves, and so forth are encouraged to attend).
A few thoughts on reinterpreting orc features...
Darkvision: If they once came from the deep sea, then it makes sense that orcs retain some way to see in the dark murky depths.
Aggressive: While their combat style could be seen as needing to rapidly ascend slopes or to quickly catch/dispatch a scout to avoid their people being discovered, there's another way to look at this. The bonus action to move toward an enemy (and CON bonus) actually makes orcs great free divers, letting them reach enemies deeper underwater or, conversely, to ambush enemies out of the water like Navy Seals.
Menacing: If you've been pushed from your homeland to a hostile place with neighbors who don't like you... If you need to win a battle without fighting a battle (because you don't have the numbers to survive a mass confrontation & you have pregnant mothers and children in your caravan)... then intimidation tactics make a lot of sense.
Powerful Build: Not unreasonable for a culture with a built in pilgrimage where you need to carry lots of gear across long distances. This also makes orcs great at portaging canoes, and lifting heavy things... including heavy stones or shipwrecked things underwater.
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