Last week, the Japanese coast guard arrested the captain of a Chinese fishing trawler after it twice collided with patrol boats in disputed waters controlled by Tokyo. Japan has chosen this moment to take a belated stand against what it sees as a pattern of Chinese bullying at sea.
In April, a large Chinese naval force ventured into waters close to Japan and a Chinese helicopter buzzed Japanese ships at a range of just 90m.
China, too, is standing firm, warning of repercussions if Japan prosecutes the captain under domestic law. Already, Beijing has called off scheduled talks about contested energy deposits in the East China Sea.
The immediate spat may be about sovereignty over the uninhabited Senkaku or, in Chinese, Diaoyu islands.
But there is much more at stake than fish and face.
This is the latest in a series of disturbances in Asian waters this year, in which the changing balance of strength and interests among the region's naval powers points to heightened risks of miscalculation and even conflict.
It is no surprise that Asia's key security interactions are at sea, given this maritime region's vast and growing reliance on seaborne commerce, especially energy imports. What is alarming is the new degree of risk that some powers, notably China, seem willing to incur in this Indo-Pacific commons.
This year's first sea of troubles was off the coast of the divided Korean peninsula.
In March, a North Korean torpedo sank the small South Korean warship Cheonan, killing 46 crewmen in an action Beijing refused to condemn. When the US and South Korea responded with massive naval wargames, Beijing objected, and the exercises were shifted to waters far from China. Beijing then held firepower exercises of its own.
Now Washington and Seoul are planning new drills, possibly bringing a US aircraft carrier into the Yellow Sea in defiance of China's protests. In a separate move, American, South Korean and Australian forces plan to hold a small-scale re-enactment today of the historic Incheon landings that turned the tide of the Korean War in 1950. This commemoration was long scheduled, but symbolises that South Korea is far from friendless in the face of continued provocations from the North.
Much of the wider regional tension involves China. Beijing is pursuing assertive deployments and uncompromising diplomacy in several maritime theatres. Beijing has declared the entire South China Sea "a core interest", on a par with Tibet and Taiwan. Recently a Chinese submarine reportedly planted a flag on the seabed. This suggests a new willingness to confront nations, such as Vietnam, in disputed waters.
In the Indian Ocean, the potential for confrontation between Beijing and New Delhi is gradually growing. On the bright side, there has been some welcome co-ordination between China's and some of the other naval taskforces patrolling against Somali pirates.
And New Delhi, rattled in 2008 by the speed of Beijing's deployment to an ocean India had long considered its own, has proposed limited maritime security co-operation with China.
But this idea may fall victim to wider differences between two rising giants, including recent arguments over their land border.
Broadly, Beijing's naval modernisation is the understandable response of a vast trading power to anxiety about its vulnerable energy supplies. It was inconceivable that China would forever outsource sea-lane security to the US.
At this time of unprecedented Chinese naval power, modernisation and audacity, it is troubling that diplomatic mechanisms for communication and preventing strife at sea remain weak to non-existent. This is as bad for China as it is for everyone else.
The increasingly crowded maritime highways of the Indo-Pacific lack even the basic code that helped keep the Cold War cool. In the early 1970s, the Americans and Soviets crafted a detailed agreement and operating rules to stop incidents at sea from escalating to war. Today, no such understanding exists between China and the other powers its navy is increasingly brushing up against.
And while Beijing, New Delhi and Japan are finally talking about setting up leadership hotlines to help cope with their security tensions, there remains much confusion about how these might work in practice. Beijing and Tokyo cannot so far even agree if their proposed military hotline would simply give warning of defence exercises or serve to manage crises in real time.
Earlier this year, China cited US arms sales to Taiwan as its reason to suspend precisely the kind of military-military dialogues with the US that both powers need to minimise accidental encounters at sea. While Beijing and Tokyo joust verbally over fishermen and islands, Chinese and American officials have been meeting to steer their own rocky relationship back on course and have hinted that defence talks might at last be restored.
For now, though, Asia's maritime leviathans are not communicating properly with each other over keeping the peace at sea, at the very time when the risks of confrontation in the region's waters are growing.
With little near-term chance of smaller countries or regional diplomatic forums having much say, the stability of Australia's wider region is at the mercy of the strong and the reckless.